Semiconductor device and method of driving the semiconductor device

ABSTRACT

Display irregularities in light emitting devices, which develop due to dispersions per pixel in the threshold value of TFTs for supplying electric current to light emitting elements, are obstacles to increasing the image quality of the light emitting devices. An electric potential in which the threshold voltage of a TFT ( 105 ) is either added to or subtracted from the electric potential of a reset signal line ( 110 ) is stored in capacitor means ( 108 ). A voltage, in which the corresponding threshold voltage is added to an image signal, is applied to a gate electrode of a TFT ( 106 ). TFTs within a pixel are disposed adjacently, and dispersion in the characteristics of the TFTs does not easily develop. The threshold value of the TFT ( 105 ) is thus cancelled, even if the threshold values of the TFTs ( 106 ) differ per pixel, and a predetermined drain current can be supplied to an EL element ( 109 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/949,317, filed Jul. 24, 2013, now allowed, which is a continuation ofU.S. application Ser. No. 12/917,528, filed Nov. 2, 2010, now U.S. Pat.No. 8,497,823, which is a divisional of U.S. application Ser. No.10/350,134, filed Jan. 24, 2003, now U.S. Pat. No. 7,924,244, whichclaims the benefit of a foreign priority application filed in Japan asSerial No. 2002-016183 on Jan. 24, 2002, all of which are incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, to a semiconductor device having atransistor and a method of driving the semiconductor device. Further,the present invention relates to an active matrix light emitting devicehaving a semiconductor device with a thin film transistor (hereinafterreferred to as a TFT) formed on an insulator such as glass or plastic,and a method of driving the semiconductor device. Also, the presentinvention relates to electronic equipment using this type of lightemitting device.

2. Description of the Related Art

The development of display devices in which light emitting elements suchas electro luminescence (EL) elements are used, has become active inrecent years. Being self-luminous, the light emitting element is high invisibility and eliminates the need for a backlight that is necessary inliquid crystal display devices (LCDs) etc., thereby being capable ofreducing the thickness of such devices. Also, the light emitting devicesmay have virtually no limit in terms of viewing angles.

The term EL element indicates an element having a light emitting layerin which luminescence generated by application of an electric field canbe obtained. There are light emission when returning to a base statefrom a singlet excitation state (fluorescence), and light emission whenreturning to a base state from a triplet excitation state(phosphorescence) in the light emitting layer. A light emitting deviceof the present invention may use either of the aforementioned types oflight emission.

EL elements normally have a laminate structure in which a light emittinglayer is sandwiched between a pair of electrodes (anode and cathode). Alaminate structure consisting of an anode, a hole transporting layer, a.light emitting layer, an electron transporting layer, and a cathode canbe given as a typical structure. Further, structures having thefollowing layers laminated in order between an anode and a cathode alsoexist: a hole injecting layer, a hole transporting layer, a lightemitting layer, and an electron transporting layer; and a hole injectinglayer, a hole transporting layer, a light emitting layer, an electrontransporting layer, and an electron injecting layer. Any of theabove-stated structures may be employed as the EL element structure usedin the light emitting device of the present invention. Furthermore,fluorescent pigments and the like may also be doped into the lightemitting layer.

Here, all layers formed in EL elements between the anode and the cathodeare referred to generically as “EL layers”. The aforementioned holeinjecting layer, hole transporting layer, light emitting layer, electrontransporting layer, and electron injecting layer are all included in thecategory of EL layers, and light emitting elements structured by ananode, an EL layer, and a cathode are referred to as EL elements.

The structure of a pixel in a general light emitting device is shown inFIG. 8. Note that an EL display device is used as an example of atypical light emitting device. The pixel shown in FIG. 8 has a sourcesignal line 801, a gate signal line 802, a switching TFT 803, a driverTFT 804, capacitor means 805, an EL element 806, an electric currentsupply line 807, and an electric power source line 808.

The connectivity relationship between each portion is explained. Theterm TFT as used here refers to a three terminal element having a gate,a source, and a drain, but it is difficult to make clear distinctionsbetween the source and the drain due to the structure of TFTs. Oneterminal, the source or the drain, is therefore denoted as a firstelectrode, and the other terminal is denoted as a second electrode whenexplaining the connections between the elements. The terms source anddrain are used in the case where a definition of the electric potentialof each element is necessary relating to on and off states of the TFT(for example, when explaining a voltage between the gate and the sourceof the TFT).

Further, the TFT being in an on state refers to a state in which thevoltage between the gate and the source of the TFT exceeds the thresholdvalue of the TFT, and electric current flows between the source and thedrain. The TFT being in an off state refers to a state in which thevoltage between the gate and the source of the TFT is less than thethreshold value of the TFT, and the electric current does not flowbetween the source and the drain. Note that there are cases in which aslight amount of the electric current, referred to as a leak current,flows between the source and the drain even if the voltage between thegate and the source of the TFT is less than the threshold value.However, this state is treated similarly to the off state.

A gate electrode of the switching TFT 803 is connected to the gatesignal line 802, a first electrode of the switching TFT 803 is connectedto the source signal line 801, and a second electrode of the switchingTFT 803 is connected to a gate electrode of the driver TFT 804. A firstelectrode of the driver TFT 804 is connected to the electric currentsupply line 807, and a second electrode of the driver TFT 804 isconnected to a first electrode of the EL element 806. A second electrodeof the EL element 806 is connected to the electric power source line808. There is a mutual electric potential difference between theelectric current supply line 807 and the electric power source line 808.Further, the capacitor means 805 may be formed between the gateelectrode of the driver TFT 804 and the line having a fixed electricpotential, such as the electric current supply line 807, in order tomaintain the voltage between the gate and the source of the driver TFT804 during light emission.

An image signal input to the source signal line 801 is then input to thegate electrode of the driver TFT 804 if a pulse is input to the gatesignal line 802 and the switching TFT 803 is on. The voltage between thegate and the source of the driver TFT 804, and the amount of theelectric current flowing between the source and the drain of the driverTFT 804 (hereinafter referred to as a drain current), are determined inaccordance with the electric potential of the input image signal. Thiselectric current is supplied to the EL element 806, and the EL element806 emits light.

TFTs formed by polycrystalline silicon (hereinafter referred to as P-Si)have a higher field-effect mobility than TFTs formed by using amorphoussilicon (hereinafter referred to as A-Si), and a larger on current, andtherefore are very suitable as transistors used in light emittingdevices.

Conversely, TFTs formed by P-Si have a problem in that dispersion intheir electrical characteristics tends to develop due to defects incrystal grain boundaries.

If there is a dispersion in TFT threshold values, for example adispersion per pixel in the threshold values of the driver TFTs 804 inFIG. 8, then a difference in the brightness of the EL elements 806develops due to dispersion in the value of the drain current of theTFTs, corresponding to the dispersion in the TFT threshold values, evenif the same image signal is input to different pixels. This particularlybecomes a problem for display devices employing an analog gray scalemethod.

It has been proposed recently that these types of TFT threshold valuedispersions can be corrected. A structure shown in FIG. 10 can be givenas one example of such as proposal (refer to patent document 1).

[Patent document 1] International Publication number 99-48403 pamphlet(p. 25, FIG. 3, FIG. 4).

A pixel shown in FIG. 10A has a source signal line 1001, first to thirdgate signal lines 1002 to 1004, TFTs 1005 to 1008, capacitor means 1009(C₂) and 1010 (C₁), an EL element 1011, an electric current supply line1012, and an electric power source line 1013.

A gate electrode of the TFT 1005 is connected to the first gate signalline 1002, a first electrode of the TFT 1005 is connected to the sourcesignal line 1001, and a second electrode of the TFT 1005 is connected toa first electrode of the capacitor means 1009. A second electrode of thecapacitor means 1009 is connected to a first electrode of the capacitormeans 1010, and a second electrode of the capacitor means 1010 isconnected to the electric current supply line 1012. A gate electrode ofthe TFT 1006 is connected to the second electrode of the capacitor means1009 and the first electrode of the capacitor means 1010, a firstelectrode of the TFT 1006 is connected to the electric current supplyline 1012, and a second electrode of the TFT 1006 is connected to afirst electrode of the TFT 1007 and a first electrode of the TFT 1008. Agate electrode of the TFT 1007 is connected to the second gate signalline 1003, and a second electrode of the TFT 1007 is connected to thesecond electrode of the capacitor means 1009. A gate electrode of theTFT 1008 is connected to the third gate signal line 1004, and a secondelectrode of the TFT 1008 is connected to a first electrode of the ELelement 1011. A second electrode of the EL element 1011 is connected tothe electric power source line 1013, and has a mutual electric potentialdifference with the electric current supply line 1012.

Operation is explained using FIGS. 10A and 10B, and FIGS. 11A to 11F.FIG. 10B shows image signals input to the source signal line 1001 andthe first to the third gate signal lines 1002 to 1004, and shows pulsetiming. FIG. 10B is divided into sections I to VIII corresponding toeach operation shown in FIGS. 11A to 11F. Further, a structure usingfour TFTs is used as an example in the pixel shown in FIGS. 10A and 10B,with all four being p-type TFTs. The TFTs therefore turn on when an Llevel signal is input to their gate electrodes, and turn off when an Hlevel signal is input. Furthermore, although image signals input to thesource signal line 1001 are shown here which have a pulse shape in orderto indicate input periods only, predetermined analog electric potentialsmay also be used for an analog gray scale method.

First, L level is input to the first and the third gate signal lines1002 and 1004, and the TFTs 1005 and 1008 turn on (section I). Thesecond gate signal line 1003 then becomes L level, and the TFT 1007turns on. Electric charge accumulates in the capacitor means 1009 and1010 as shown in FIG. 11A. The TFT 1006 turns on at the point when anelectric potential difference between both electrodes of the capacitormeans 1010, in other words, when a voltage maintained in the capacitormeans 1010, exceeds a threshold value |V_(th)| of the TFT 1006 (sectionII).

The third gate signal line 1004 then becomes H level, and the TFT 1008turns off. The electric charge which has accumulated in the capacitormeans 1009 and 1010 thus moves once again, and the voltage stored in thecapacitor means 1010 soon becomes equal to |V_(th)|. The electricpotential of the electric current supply line 1012 and the electricpotential of the source signal line 1001 are both an electric potentialV_(DD) at this point, as shown in FIG. 11B, and therefore the voltagemaintained in the capacitor means 1009 also becomes equal to |V_(th)|.The TFT 1006 therefore soon turns off.

The second gate signal line 1003 becomes H level after the voltagesmaintained in the capacitor means 1009 and 1010 become equal to|V_(th)|, as discussed above, and the TFT 1007 turns off (section IV).|V_(th)| is thus stored in the capacitor means 1009 by this operation,as shown in FIG. 11C.

A relationship like that of Eq. (1) results for an electric charge Q₁stored at this point in the capacitor means 1010 (C₁). Similarly, arelationship like that of Eq. (2) results for an electric charge Q₂stored at this point in the capacitor means 1009 (C₂).

[Eq.  (1)]                                        $\begin{matrix}{{Q_{1} = {C_{1} \times {{V_{th}}\left\lbrack {{Eq}.\mspace{14mu}(2)} \right\rbrack}}}\mspace{635mu}} & (1) \\{Q_{2} = {C_{2} \times {V_{th}}}} & (2)\end{matrix}$

Input of an image signal is then performed as shown in FIG. 11D (sectionV). The image signal is output to the source signal line 1001, and theelectric potential of the source signal line 1001 changes from theelectric potential V_(DD) to an electric potential V_(Data) of the imagesignal (the TFT 1006 is a p-channel TFT here, and thereforeV_(DD)>V_(Data)). If the electric potential of the gate electrode of theTFT 1006 is taken as an electric potential V_(P), and the electriccharge in the node is taken as Q, then relationships like those of Eq.(3) and Eq. (4) develop due to conservation law of charge including thecapacitor means 1009 and 1010.

[Eq.  (3)]                                        $\begin{matrix}{{{Q + Q_{1}} = {C_{1} \times {\left( {V_{DD} - V_{P}} \right)\left\lbrack {{Eq}.\mspace{14mu}(4)} \right\rbrack}}}\mspace{619mu}} & (3) \\{{Q - Q_{2}} = {C_{2} \times \left( {V_{P} - V_{Data}} \right)}} & (4)\end{matrix}$

From Eqs. (1) to (4), the electric potential V_(P) of the gate electrodeof the TFT 1006 can be expressed by Eq. (5).

[Eq.  (5)]                                        $\begin{matrix}{V_{P} = {{\frac{C_{1}}{C_{1} + C_{2}}V_{DD}} + {\frac{C_{2}}{C_{1} + C_{2}}V_{Data}} - {V_{th}}}} & (5)\end{matrix}$

A voltage V_(GS) between the gate and the source of the TFT 1006 istherefore expressed by Eq. (6).

[Eq.  (6)]                                        $\begin{matrix}\begin{matrix}{V_{GS} = {V_{P} - V_{DD}}} \\{= {{\frac{C_{2}}{C_{1} + C_{2}}\left( {V_{Data} - V_{DD}} \right)} - {V_{th}}}} \\{= {{\frac{C_{2}}{C_{1} + C_{2}}\left( {V_{Data} - V_{DD}} \right)} + V_{th}}}\end{matrix} & (6)\end{matrix}$

The term V_(th) is contained in the right-hand side of Eq. (6). That is,the threshold voltage of the TFT 1006 in each pixel is added to theimage signal input from the source signal line 1001, and this is storedby the capacitor means 1009 and 1010.

The first gate signal line 1002 becomes H level when the input of theimage signal is complete, and the TFT 1005 turns off (section VI). Thesource signal line 1001 then returns to a predetermined electricpotential (section VII). Operations for writing in the image signal tothe pixels are thus complete (FIG. 11E).

The third gate signal line 1004 then becomes L level, the TFT 1008 turnson, and the EL element 1011 emits light due to electric current flowingin the EL element 1011, as shown in FIG. 11F. The amount of electriccurrent flowing in the EL element 1011 at this point depends upon thevoltage between the gate and the source of the TFT 1006, and a draincurrent I_(DS) flowing in the TFT 1006 is expressed by Eq. (7).

[Eq.  (7)]                                        $\begin{matrix}\begin{matrix}{I_{DS} = {\frac{\beta}{2}\left( {V_{GS} - V_{th}} \right)^{2}}} \\{= {\frac{\beta}{2}\left\{ {\frac{C_{2}}{C_{1} + C_{2}}\left( {V_{Data} - V_{DD}} \right)} \right\}^{2}}}\end{matrix} & (7)\end{matrix}$

It can be seen from Eq. (7) that the drain current I_(DS) of the TFT1006 does not depend on the threshold value V_(th). The value of theelectric current flowing in the EL elements 1011 of each of the pixelstherefore does not change, even if there is dispersion in the thresholdvalues of the TFTs 1006 in each of the pixels. Electric currenttherefore flows correctly in the EL elements 1011 in accordance with theimage signal V_(Data).

However, the drain current I_(DS) in Eq. (7) does depend upon thecapacitances C₁ and C₂ with the aforementioned structure. That is, thedrain current I_(DS) will have dispersion if the capacitance values ofthe capacitor means 1009 and 1010 have dispersion.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide asemiconductor device capable of correcting dispersions in TFT thresholdvalues due to the aforementioned problem, specifically a semiconductordevice having a structure that is not influenced by dispersions incapacitance values. In addition, an object of the present invention isto provide a method of driving the semiconductor device.

Operating principles of the present invention are explained using FIGS.14A to 14E. Consider circuits like those of FIG. 14A or 14B. Switchingelements 1403 and 1413 are elements that are controlled by inputsignals, and may be elements capable of being placed in a conductive ora non-conductive state. For example, elements such as TFTs, with whichon and off can be selected by an input signal, may be employed.

Further, an element in which electric current develops only in a singledirection when an electric potential difference is imparted to bothelectrodes of the element is defined as a rectifying element. Diodes andTFTs having a short circuit between their gate and drain (this state isdenoted as a diode connection) can be given as examples of rectifyingelements.

Consider circuits in which the switching elements 1403 and 1413,capacitor means 1402 and 1412, and rectifying elements 1401 and 1411 areconnected as shown in FIGS. 14A and 14B. The rectifying element 1401uses a p-channel TFT, and the rectifying element 1411 uses an n-channelTFT.

Terminals in each circuit are denoted by α, β, γ, and δ. Fixed electricpotentials are imparted to each of the terminals α to γ. The electricpotential imparted to the terminals α and β in FIG. 14A is taken asV_(SS), and the electric potential imparted to the terminal γ is takenas V_(Reset) (V_(Reset)≧V_(SS)+|V_(th)P|, where V_(th)P is the thresholdvalue of the rectifying element 1401). The electric potential impartedto the terminals α and β for the case of FIG. 14B is taken as V_(x), andthe electric potential imparted to the terminal γ is taken as V_(Reset)(V_(Reset)≦V_(x)−|V_(th)N|, where V_(th)N is the threshold value of therectifying element 1411).

The switching elements 1403 and 1413 are conductive during a perioddenoted by symbol i in FIG. 14C. In FIG. 14A, the electric potential ofa gate electrode and a drain electrode of the TFT 1401, which is arectifying element, drops to become V_(SS) in FIG. 14A. On the otherhand, in FIG. 14B, the electric potential of a gate electrode and adrain electrode of the TFT 1411, which is a rectifying element,increases to become V_(x). The voltage between the source and the drainof both the TFT 1401 and the TFT 1411 is higher than the absolute valueof the threshold voltage, and therefore both turn on.

The switching elements 1403 and 1413 then become non-conductive during aperiod denoted by symbol ii in FIG. 14C. The TFTs 1401 and 1411 are bothon at this point, and electric current develops in each between theirsource and drain. The electric potential of the gate electrode and thedrain electrode of the TFT 1401 increases in FIG. 14A, and the electricpotential of the gate electrode and the drain electrode of the TFT 1411drops in FIG. 14B. The voltage between the source and the drain of theTFT 1401 and the voltage between the source and the drain of the TFT1411, in other words the voltages between the gate and the source of theTFTs 1401 and 1411, therefore become smaller.

The voltages between the gate and the source of the TFTs 1401 and 1411each therefore become equal to the threshold value of their respectiveTFTs. The TFTs 1401 and 1411 therefore turn off. The electric potentialdifferences between the electric potential of the drain electrode of theTFTs 1401 and 1411, and the terminal α are stored by the capacitor means1402 and 1412 at this point.

V_(Reset)−|V_(th)P| is therefore output from the terminal δ in FIG. 14Aduring a period denoted by symbol iii in FIG. 14C, andV_(Reset)+|V_(th)N| is output from the terminal δ in FIG. 14B.

It can be seen that the threshold voltage of the TFTs 1401 and 1411 canbe output for both FIG. 14A and FIG. 14B. For example, if a signal isinput to the terminal α in this state, then capacitive coupling occursby the capacitor means 1402 and 1412, and the electric potential of theterminal δ changes by the amount of the voltage of the input signal. TheTFT threshold voltage already appears at the terminal δ, and thereforethere is a correction applied with respect to the signal input by theamount of the TFT threshold voltage.

A different structure having the same operating principle may also beused as shown in FIGS. 14D and 14E, in which a diode 1410 or capacitormeans 1420 is formed as a substitute for the switching element 1403, andthe electric potential of the gate electrode and the drain electrode ofthe TFT 1401 is lowered by reducing the electric potential of theterminal β (V_(SS) here). The electric potential of the terminal δ atthis point can drop to V_(SS)+|V_(th)D|, where V_(th)D is the thresholdvalue of the diode 1410). Electric current does not flow in the reversedirection in the case of FIG. 14D provided that the electric potentialof the terminal β is increased (V_(DD) here) after the electricpotential of the gate electrode and the drain electrode of the TFT 1401are initially reduced, and this therefore becomes similar to making aswitching element non-conductive.

Note that although the TFT 1401 uses a p-channel TFT here, it may alsouse an n-channel TFT. In this case, the drain electrode and the gateelectrode of the TFT 1401 are connected to the terminal γ side.Similarly, although the TFT 1411 uses an n-channel 111, it may also usea p-channel TFT. The drain electrode and the gate electrode of the TFT1411 are then connected to the terminal γ side for this case.

Further, the TFTs 1401 and 1411 may also use diodes. For the diodes tobe used here, in addition to diodes having a normal p-n junction, TFTshaving the aforementioned diode connection may also be used.

Correcting dispersion in TFT threshold values in a light emittingdevice, and reducing dispersion in the brightness of EL elements aretaken as objectives here and methods for accomplishing the objectivesare explained; The operating principle of the present invention is notlimited to the correction of dispersion in TFT threshold values,however, and of course it is also possible to apply the presentinvention to other electronic circuits.

Structures of the present invention are discussed below.

According to the present invention, there is provided a semiconductordevice comprising:

-   -   a rectifying element;    -   capacitor means; and    -   a switching element,

characterized in that:

-   -   a first electrode of the rectifying element is electrically        connected to a first electrode of the capacitor means and a        first electrode of the switching element.

According to the present invention, there is provided a semiconductordevice comprising:

-   -   a first rectifying element having a first electrode;    -   a second rectifying element having a first electrode; and    -   capacitor means,

characterized in that:

-   -   a first electrode of the first rectifying element electrically        connected to a first electrode of the capacitor means and a        first electrode of the second rectifying element.

According to the present invention, there is provided a semiconductordevice comprising:

-   -   a rectifying element;    -   capacitor means; and    -   a switching element,

characterized in that:

-   -   an electric potential V₁ of a first electric power source is        imparted to a first electrode of the rectifying element;    -   a second electrode of the rectifying element is electrically        connected to a first electrode of the capacitor means and a        first electrode of the switching element;    -   an electric potential V₂ of a second electric power source is        imparted to a second electrode of the switching element;    -   a signal having an electric potential that is greater than or        equal to an electric potential V₃ and less than or equal to        (V₃+an electric potential V_(Data)), or greater than or equal to        (V₃−V_(Data)) and less than or equal to V₃, is input to a second        electrode of the capacitor means; and    -   a signal having an electric potential equal to any one of        (V₁+|V_(th)|), and (V₁+|V_(th)|±V_(Data)) is obtained from the        second electrode of the rectifying element when a threshold        voltage of the rectifying element is taken as V_(th).

According to the present invention, there is provided a semiconductordevice comprising:

-   -   a rectifying element;    -   capacitor means; and    -   a switching element,

characterized in that:

-   -   an electric potential V₁ of a first electric power source is        imparted to a first electrode of the rectifying element;    -   a second electrode of the rectifying element is electrically        connected to a first electrode of the capacitor means and a        first electrode of the switching element;    -   an electric potential V₂ of a second electric power source is        imparted to a second electrode of the switching element;    -   a signal having an electric potential that is greater than or        equal to an electric potential V₃ and less than or equal to        (V₃+an electric potential V_(Data)), or greater than or equal to        (V₃−V_(Data)) and less than or equal to V₃, is input to a second        electrode of the capacitor means; and    -   a signal having an electric potential equal to any one of        (V₁−|V_(th)|), V₂, and (V₁−|V_(th)|±V_(data)) is obtained from        the second electrode of the rectifying element when a threshold        voltage of the rectifying element is taken as V_(th).

According to the present invention, there is provided a semiconductordevice comprising:

-   -   a first rectifying element;    -   a second rectifying element; and    -   capacitor means,

characterized in that:

-   -   an electric potential V₁ of a first electric power source is        imparted to a first electrode of the first rectifying element;    -   a second electrode of the first rectifying element is        electrically connected to a first electrode of the capacitor        means and a first electrode of the second rectifying element;    -   a first signal having an electric potential greater than or        equal to an electric potential V₂ and less than or equal to an        electric potential V₂′ is input to a second electrode of the        second rectifying element;    -   a second signal having an electric potential that is greater        than or equal to an electric potential V₃ and less than or equal        to (V₃+an electric potential V_(Data)), or greater than or equal        to (V₃−V_(Data)) and less than or equal to V₃, is input to a        second electrode of the capacitor means; and    -   a signal having an electric potential equal to any one of        (V₁−|V_(th)1|), (V₂+V_(th)2), and (V₁−|V_(th)1|±V_(Data)) is        obtained from the second electrode of the first rectifying        element when a threshold voltage of the first rectifying element        is taken as V_(th)1 and a threshold voltage of the second        rectifying element is taken as V_(th)2.

According to the present invention, there is provided a semiconductordevice comprising:

-   -   a first rectifying element;    -   a second rectifying element; and    -   capacitor means,

characterized in that:

-   -   an electric potential V₁ of a first electric power source is        imparted to the first electrode of the first rectifying element;    -   a second electrode of the first rectifying element is        electrically connected to a first electrode of the capacitor        means and a first electrode of the second rectifying element;    -   a first signal having a voltage amplitude of an electric        potential greater than or equal to an electric potential V₂ and        less than or equal to an electric potential V₂′ is input to a        second electrode of the second rectifying element;    -   a second signal having an electric potential that is greater        than or equal to an electric potential V₃ and less than or equal        to (V₃+an electric potential V_(Data)), or greater than or equal        to (V₃−V_(Data)) and less than or equal to V₃, is input to a        second electrode of the capacitor means; and    -   a signal having an electric potential equal to any one of        (V₁+V_(th)1), (V₂′−V_(th)2), and (V₁+V_(th)1±V_(Data)) is        obtained from the second electrode of the first rectifying        element when a threshold voltage of the first rectifying element        is taken as V_(th)1 and a threshold voltage of the second        rectifying element is taken as V_(th)2.

According to the present invention, there is provided a semiconductordevice, characterized in that:

-   -   the rectifying element is formed by using a transistor having a        connection between its gate and its drain;    -   V₁<V₂ if the transistor having a connection between its gate and        its drain is an n-channel transistor; and    -   V₁>V₂ if the transistor having a connection between its gate and        its drain is a p-channel transistor.

According to the present invention, there is provided a semiconductordevice, characterized in that:

-   -   the first rectifying element is formed by using a transistor        having a connection between its gate and its drain;    -   V₁<V₂ if the transistor having a connection between its gate and        its drain is an n-channel transistor; and    -   V₁>V₂ if the transistor having a connection between its gate and        its drain is a p-channel transistor.

According to the present invention, there is provided a semiconductordevice, further comprising a transistor, characterized in that a gateelectrode of the transistor is electrically connected to the firstelectrode of the capacitor means.

According to the present invention, there is provided a semiconductordevice comprising a plurality of pixels, each pixel including:

-   -   a source signal line;    -   a first gate signal line;    -   a second gate signal line;    -   a reset electric power source line;    -   an electric current supply line;    -   a first transistor,    -   a second transistor;    -   a third transistor;    -   a fourth transistor;    -   capacitor means; and    -   a light emitting element,

characterized in that:

-   -   a gate electrode of the first transistor is electrically        connected to the first gate signal line;    -   a first electrode of the first transistor is electrically        connected to the source signal line;    -   a second electrode of the first transistor is electrically        connected to a first electrode of the capacitor means;    -   a second electrode of the capacitor means is electrically        connected to a gate electrode of the second transistor, a first        electrode of the second transistor, and a gate electrode of the        third transistor;    -   a second electrode of the second transistor is electrically        connected to the reset electric power source line;    -   a first electrode of the third transistor is electrically        connected to the electric current supply line;    -   a second electrode of the third transistor is electrically        connected to a first electrode of the light emitting element;    -   a gate electrode of the fourth transistor is electrically        connected to the second gate signal line;    -   a first electrode of the fourth transistor is electrically        connected to the source signal line or the second electrode of        the first transistor; and    -   a second electrode of the fourth transistor is electrically        connected to the gate electrode of the second transistor, the        first electrode of the second transistor, and the gate electrode        of the third transistor.

According to the present invention, there is provided a semiconductordevice comprising a plurality of pixels, each pixel including:

-   -   a source signal line;    -   a first gate signal line;    -   a second gate signal line;    -   a reset electric power source line;    -   an electric current supply line;    -   a first transistor;    -   a second transistor;    -   a third transistor;    -   capacitor means;    -   a diode; and    -   a light emitting element,

characterized in that:

-   -   a gate electrode of the first transistor is electrically        connected to the first gate signal line;    -   a first electrode of the first transistor is electrically        connected to the source signal line;    -   a second electrode of the first transistor is electrically        connected to a first electrode of the capacitor means;    -   a second electrode of the capacitor means is electrically        connected to a gate electrode of the second transistor, a first        electrode of the second transistor, and a gate electrode of the        third transistor;    -   a second electrode of the second transistor is electrically        connected to the reset electric power source line;    -   a first electrode of the third transistor is electrically        connected to the electric current supply line;    -   a second electrode of the third transistor is electrically        connected to a first electrode of the light emitting element;    -   a first electrode of the diode is electrically connected to the        gate electrode of the second transistor, the first electrode of        the second transistor, and the gate electrode of the third        transistor; and    -   a second electrode of the diode is electrically connected to the        second gate signal line.

According to the present invention, there is provided a semiconductordevice comprising a plurality of pixels, each pixel including:

-   -   a source signal line;    -   a first gate signal line;    -   a second gate signal line;    -   a reset electric power source line;    -   an electric current supply line;    -   a first transistor,    -   a second transistor;    -   a third transistor,    -   a first capacitor means;    -   a second capacitor means; and    -   a light emitting element,

characterized in that:

-   -   a gate electrode of the first transistor is electrically        connected to the first gate signal line;    -   a first electrode of the first transistor is electrically        connected to the source signal line;    -   a second electrode of the first transistor is electrically        connected to a first electrode of the first capacitor means;    -   a second electrode of the first capacitor means is electrically        connected to a gate electrode of the second transistor, a first        electrode of the second transistor, and a gate electrode of the        third transistor;    -   a second electrode of the second transistor is electrically        connected to the reset electric power source line;    -   a first electrode of the third transistor is electrically        connected to the electric current supply line;    -   a second electrode of the third transistor is electrically        connected to a light emitting element;

a first electrode of the second capacitor means is electricallyconnected to the gate electrode of the second transistor, the firstelectrode of the second transistor, and the gate electrode of the thirdtransistor; and

-   -   a second electrode of the second capacitor means is electrically        connected to the second gate signal line.

According to the present invention, there is provided a semiconductordevice comprising a plurality of pixels, each pixel including:

-   -   a source signal line;    -   a first gate signal line;    -   a second gate signal line;    -   a third gate signal line;    -   a reset electric power source line;    -   an electric current supply line;    -   a first transistor;    -   a second transistor;    -   a third transistor;    -   a fourth transistor;    -   a fifth transistor;    -   a first capacitor means;    -   a second capacitor means; and    -   a light emitting element,

characterized in that:

-   -   a gate electrode of the first transistor is electrically        connected to the first gate signal line;    -   a first electrode of the first transistor is electrically        connected to the source signal line;    -   a second electrode of the first transistor is electrically        connected to a first electrode of the first capacitor means;    -   a second electrode of the first capacitor means is electrically        connected to a gate electrode of the second transistor, a first        electrode of the second transistor, and a gate electrode of the        third transistor;    -   a second electrode of the second transistor is electrically        connected to the reset electric power source line;    -   a first electrode of the third transistor is electrically        connected to the electric current supply line;    -   a second electrode of the third transistor is electrically        connected to a light emitting elements;    -   a gate electrode of the fourth transistor is electrically        connected to the second gate signal line;    -   a first electrode of the fourth transistor is electrically        connected to the source signal line or the second electrode of        the first transistor;    -   a second electrode of the fourth transistor is electrically        connected to the gate electrode of the second transistor, the        first electrode of the second transistor, and the gate electrode        of the third transistor;    -   a first electrode of the second capacitor means is electrically        connected to the second electrode of the first transistor;    -   a second electrode of the second capacitor means is electrically        connected to the second electrode of the third transistor;    -   a gate electrode of the fifth transistor is electrically        connected to the third gate signal line;    -   a first electrode of the fifth transistor is electrically        connected to the second electrode of the third transistor, and    -   a second electrode of the fifth transistor is connected to an        electric power source electric potential that is equal to or        lower than an electric potential of a second electrode of the        light emitting element.

According to the present invention, there is provided a semiconductordevice, further comprising:

-   -   an erasure gate signal line; and    -   an erasure transistor,

characterized in that:

-   -   a gate electrode of the erasure transistor is electrically        connected to the erasure gate signal line;    -   a first electrode of the erasure transistor is electrically        connected to the electric current supply line; and    -   the second electrode of the erasure transistor is electrically        connected to the gate electrode of the third transistor.

According to the present invention, there is provided a semiconductordevice, further comprising:

-   -   an erasure gate signal line; and    -   an erasure transistor,

characterized in that:

-   -   a gate electrode of the erasure transistor is electrically        connected to the erasure gate signal line;    -   a first electrode of the erasure transistor is electrically        connected to the electric current supply line; and    -   a second electrode of the erasure transistor is electrically        connected to the second electrode of the first transistor.

According to the present invention, there is provided a semiconductordevice, further comprising:

-   -   an erasure gate signal line; and    -   an erasure transistor,

characterized in that:

-   -   the erasure transistor is formed between the electric current        supply line and the first electrode of the third transistor, or        between the second electrode of the third transistor and the        first electrode of the light emitting element; and    -   a gate electrode of the erasure transistor is electrically        connected to the erasure gate signal line.

According to the present invention, there is provided a semiconductordevice, characterized in that the second transistor and the thirdtransistor have the same polarity.

According to the present invention, there is provided a method ofdriving a semiconductor device, the semiconductor device comprising:

-   -   a rectifying element;    -   capacitor means; and    -   a switching element,

characterized in that:

-   -   an electric potential V₁ of a first electric power source is        imparted to a first electrode of the rectifying element;    -   a second electrode of the rectifying element is electrically        connected to a first electrode of the capacitor means and a        first electrode of the switching element; and    -   an electric potential V₂ of a second electric power source is        imparted to a second electrode of the switching element;

the method of driving the semiconductor device comprising:

-   -   when a threshold voltage of the rectifying element is taken as        V_(th),    -   a first step of making the switching element conductive and        setting the electric potential of a second electrode of the        rectifying element to V₂; and    -   a second step of making the switching element non-conductive,        making the voltage between both electrodes of the rectifying        element converge to the threshold voltage V_(th), and setting        the electric potential of the second electrode of the rectifying        element to (V₁+V_(th)).

According to the present invention, there is provided a method ofdriving a semiconductor device, the semiconductor device comprising:

-   -   a rectifying element;    -   capacitor means; and    -   a switching element,

characterized in that:

-   -   an electric potential V₁ of a first electric power source is        imparted to a first electrode of the rectifying element;    -   a second electrode of the rectifying element is electrically        connected to the first electrode of the capacitor means and a        first electrode of the switching element;    -   an electric potential V₂ of a second electric power source is        imparted to a second electrode of the switching element; and    -   a signal having an electric potential that is greater than or        equal to an electric potential V₃ and less than or equal to        (V₃+an electric potential V_(Data)), or greater than or equal to        (V₃−V_(Data)) and less than or equal to V₃, is input to a second        electrode of the capacitor means;

the method of driving the semiconductor device comprising:

-   -   when a threshold voltage of the rectifying element is taken as        V_(th),    -   a first step of making the switching element conductive and        setting the electric potential of a second electrode of the        rectifying element to V₂;    -   a second step of making the switching element non-conductive,        making the voltage between both electrodes of the rectifying        element converge to the threshold voltage V_(th), and setting        the electric potential of the second electrode of the rectifying        element to (V₁+V_(th)); and    -   a third step of changing the electric potential of the second        electrode of the capacitor means by V_(Data), and setting the        electric potential of the second electrode of the rectifying        element to (V₁+V_(th)±V_(Data)).

According to the present invention, there is provided a method ofdriving a semiconductor device, the semiconductor device comprising:

-   -   a rectifying element;    -   capacitor means; and    -   a switching element,

characterized in that:

-   -   an electric potential V₁ of a first electric power source is        imparted to a first electrode of the rectifying element;    -   a second electrode of the rectifying element is electrically        connected to a first electrode of the capacitor means and a        first electrode of the switching element; and    -   an electric potential V₂ of a second electric power source is        imparted to a second electrode of the switching element;

the method of driving the semiconductor device comprising:

-   -   when a threshold voltage of the rectifying element is taken as        V_(th),    -   a first step of making the switching element conductive and        setting the electric potential of the second electrode of the        rectifying element to V₂; and    -   a second step of making the switching element non-conductive,        making the voltage between both electrodes of the rectifying        element converge to the threshold voltage V_(th), and setting        the electric potential of the second electrode of the rectifying        element to (V₁−|V_(th)|).

According to the present invention, there is provided a method ofdriving a semiconductor device, the semiconductor device comprising:

-   -   a rectifying element;    -   capacitor means; and    -   a switching element,

characterized in that:

-   -   an electric potential V₁ of a first electric power source is        imparted to a first electrode of the rectifying element;    -   a second electrode of the rectifying element is electrically        connected to a first electrode of the capacitor means and a        first electrode of the switching element;    -   an electric potential V₂ of a second electric power source is        imparted to a second electrode of the switching element; and    -   a signal having an electric potential that is greater than or        equal to an electric potential V₃ and less than or equal to        (V₃+an electric potential V_(Data)), or greater than or equal to        (V₃−V_(Data)) and less than or equal to V₃, is input to a second        electrode of the capacitor means;

the method of driving the semiconductor device comprising:

-   -   when a threshold voltage of the rectifying element is taken as        V_(th),    -   a first step of making the switching element conductive and        setting the electric potential of the second electrode of the        rectifying element to V₂;    -   a second step of making the switching element non-conductive,        making the voltage between both electrodes of the rectifying        element converge to the threshold voltage V_(th), and setting        the electric potential of the second electrode of the rectifying        element to (V₁−|V_(th)|); and    -   a third step of changing the electric potential of the second        electrode of the capacitor means by V_(Data), and setting the        electric potential of the second electrode of the rectifying        element to (V₁−|V_(th)|±V_(Data)).

According to the present invention, there is provided a method ofdriving a semiconductor device, characterized in that:

-   -   the semiconductor device further comprises a transistor; and    -   a gate electrode of the transistor is electrically connected to        the second electrode of the rectifying element.

According to the present invention, there is provided a method ofdriving a semiconductor device, the semiconductor device comprising:

-   -   a first rectifying element having a first electrode and a second        electrode;    -   a second rectifying element having a first electrode and a        second electrode; and capacitor means,

characterized in that:

-   -   an electric potential V₁ of a first electric power source is        imparted to a first electrode of the first rectifying element;    -   a second electrode of the first rectifying element is        electrically connected to a first electrode of the capacitor        means and a first electrode of the second rectifying element;        and    -   a first signal having an electric potential greater than or        equal to an electric potential V₂ and less than or equal to an        electric potential V₂′ is input to a second electrode of the        second rectifying element;

the method of driving the semiconductor device comprising:

-   -   when a threshold voltage of the first rectifying element is        taken as V_(th)1 and a threshold voltage of the second        rectifying element is taken as V_(th)2,    -   a first step of setting the electric potential of a second        electrode of the second capacitor means to V₂, and setting the        electric potential of the second electrode of the first        rectifying element to (V₂+V_(th)2); and    -   a second step of setting the electric potential of a second        electrode of the second capacitor means to V₂′, making the        voltage between both electrodes of the first rectifying element        converge to the threshold voltage V_(th)1, and setting the        electric potential of the second electrode of the first        rectifying element to (V₁−|V_(th)1|).

According to the present invention, there is provided a method ofdriving a semiconductor device, the semiconductor device comprising:

-   -   a first rectifying element;    -   a second rectifying element; and    -   capacitor means,

characterized in that:

-   -   an electric potential V₁ of a first electric power source is        imparted to a first electrode of the first rectifying element;    -   a second electrode of the first rectifying element is        electrically connected to a first electrode of the capacitor        means and a first electrode of the second rectifying element;    -   a first signal having an electric potential greater than or        equal to an electric potential V₂ and less than or equal to an        electric potential V₂′ is input to a second electrode of the        second rectifying element; and    -   a second signal having an electric potential that is greater        than or equal to an electric potential V₃ and less than or equal        to (V₃+an electric potential V_(Data)), or greater than or equal        to (V₃−V_(Data)) and less than or equal to V₃, is input to a        second electrode of the capacitor means;

the method of driving the semiconductor device comprising:

-   -   when a threshold voltage of the first rectifying element is        taken as V_(th)1 and a threshold voltage of the second        rectifying element is taken as V_(th)2,    -   a first step of setting the electric potential of the second        electrode of the second capacitor means to V₂, and setting the        electric potential of the second electrode of the first        rectifying element to (V₂+V_(th)2);    -   a second step of setting the electric potential of a second        electrode of the second capacitor means to V₂′, making the        voltage between both electrodes of the first rectifying element        converge to the threshold voltage V_(th)1, and setting the        electric potential of the second electrode of the first        rectifying element to (V₁−|V_(th)1|); and    -   a third step of changing the electric potential of the second        electrode of the capacitor means by V_(Data), and setting the        electric potential of the second electrode of the first        rectifying element to (V₁−|V_(th)1)±V_(Data)).

According to the present invention, there is provided a method ofdriving a semiconductor device, the semiconductor device comprising:

-   -   a first rectifying element;    -   a second rectifying element; and    -   capacitor means;

characterized in that:

-   -   an electric potential V₁ of a first electric power source is        imparted to the first electrode of the first rectifying element;    -   a second electrode of the first rectifying element is        electrically connected to a first electrode of the capacitor        means and a first electrode of the second rectifying element;        and    -   a first signal having an electric potential greater than or        equal to an electric potential V₂ and less than or equal to an        electric potential V₂′ is input to a the second electrode of the        second rectifying element;

the method of driving the semiconductor device comprising:

-   -   when a threshold voltage of the first rectifying element is        taken as V_(th)1 and a threshold voltage of the second        rectifying element is taken as V_(th)2,    -   a first step of setting the electric potential of a second        electrode of the second capacitor means to V₂,′ and setting the        electric potential of the second electrode of the first        rectifying element to (V₂′−|V_(th)2|); and    -   a second step of setting the electric potential of a second        electrode of the second capacitor means to V₂, making the        voltage between both electrodes of the first rectifying element        converge to the threshold voltage V_(th)1, and setting the        electric potential of the second electrode of the first        rectifying element to (V₁+V_(th)1).

According to the present invention, there is provided a method ofdriving a semiconductor device, the semiconductor device comprising:

-   -   a first rectifying element;    -   a second rectifying element; and    -   capacitor means,

characterized in that:

-   -   an electric potential V₁ of a first electric power source is        imparted to a first electrode of the first rectifying element;    -   a second electrode of the first rectifying element is        electrically connected to a first electrode of the capacitor        means and a first electrode of the second rectifying element;    -   a first signal having an electric potential greater than or        equal to an electric potential V₂ and less than or equal to an        electric potential V₂′ is input to a second electrode of the        second rectifying element; and    -   a second signal having an electric potential that is greater        than or equal to an electric potential V₃ and less than or equal        to (V₃+an electric potential V_(Data)), or greater than or equal        to (V₃−V_(Data)) and less than or equal to V₃, is input to a        second electrode of the capacitor means;

the method of driving the semiconductor device comprising:

-   -   when a threshold voltage of the first rectifying element is        taken as V_(th)1 and a threshold voltage of the second        rectifying element is taken as V_(th)2,    -   a first step of setting the electric potential of the second        electrode of the second capacitor means to V₂′, and setting the        electric potential of the second electrode of the first        rectifying element to (V₂′−|V_(th)2|);    -   a second step of setting the electric potential of a second        electrode of the second capacitor means to V₂, making the        voltage between both electrodes of the first rectifying element        converge to the threshold voltage V_(th)1, and setting the        electric potential of the second electrode of the first        rectifying element to (V₁+V_(th)1); and    -   a third step of changing the electric potential of the second        electrode of the capacitor means by V_(Data), and setting the        electric potential of the second electrode of the first        rectifying element to (V₁+V_(th)1±V_(Data)).

According to the present invention, there is provided a method ofdriving a semiconductor device, characterized in that:

-   -   the semiconductor device further comprises a transistor; and    -   a gate electrode of the transistor is electrically connected to        the second electrode of the first rectifying element.

According to the present invention, there is provided a method ofdriving a semiconductor device, characterized in that:

-   -   the rectifying element is formed by using a transistor having a        connection between its gate and its drain;    -   V₁<V₂ if the transistor having a connection between its gate and        its drain is an n-channel transistor; and    -   V₁>V₂ if the transistor having a connection between its gate and        its drain is a p-channel transistor.

According to the present invention, there is provided a method ofdriving a semiconductor device, characterized in that:

-   -   the first rectifying element is formed by using a transistor        having a connection between its gate and its drain;    -   V₁<V₂ if the transistor having a connection between its gate and        its drain is an n-channel transistor; and    -   V₁>V₂ if the transistor having a connection between its gate and        its drain is a p-channel transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are diagrams for explaining an embodiment mode of thepresent invention, and operation of the embodiment mode;

FIGS. 2A to 2E are diagrams for explaining an embodiment mode of thepresent invention, and operation of the embodiment mode;

FIGS. 3A to 3E are diagrams for explaining an embodiment mode of thepresent invention, and operation of the embodiment mode;

FIGS. 4A to 4C are diagrams for explaining an embodiment mode of thepresent invention, and operation of the embodiment mode;

FIGS. 5A to 5C are diagrams for explaining an embodiment mode of thepresent invention, and operation of the embodiment mode;

FIGS. 6A to 6C are diagrams for explaining an embodiment mode of thepresent invention, and operation of the embodiment mode;

FIGS. 7A to 7D are diagrams for explaining an embodiment mode of thepresent invention, and operation of the embodiment mode;

FIG. 8 is a diagram showing the structure of a pixel in a general lightemitting device;

FIGS. 9A to 9C are diagrams for explaining a method combining a digitalgray scale method and a time gray scale method;

FIGS. 10A and 10B are diagrams for explaining an example of a pixel of alight emitting device capable of correcting dispersions in TFT thresholdvalues, and operation of the light emitting device pixel;

FIGS. 11A to 11F are diagrams for explaining an example of a pixel of alight emitting device capable of correcting dispersions in TFT thresholdvalues, and operation of the light emitting device pixel;

FIGS. 12A to 12C are diagrams for explaining operation when a methodcombining a digital gray scale method and a time gray scale method isused in the present invention;

FIGS. 13A to 13H are diagrams showing examples of electronic equipmentcapable of applying the present invention;

FIGS. 14A to 14E are diagrams for explaining the operating principle ofthe present invention;

FIGS. 15A to 15C are an upper surface diagram and cross sectionaldiagrams of a light emitting device;

FIGS. 16A and 16B are diagrams for explaining an embodiment mode of thepresent invention, and operation of the embodiment mode;

FIGS. 17A to 17E are diagrams for explaining an embodiment mode of thepresent invention, and operation of the embodiment mode;

FIGS. 18A to 18C are diagrams for explaining an outline of a lightemitting device using an analog signal method;

FIGS. 19A and 19B are diagrams showing examples of the structure of asource signal line driver circuit and a gate signal line driver circuit,respectively, used in FIGS. 18A to 18C;

FIGS. 20A and 20B are diagrams for explaining an outline of a lightemitting device using a digital signal method;

FIGS. 21A and 21B are diagrams showing examples of the structure of asource signal line driver circuit and a gate signal line driver circuit,respectively, used in FIGS. 20A to 20C;

FIG. 22 is a diagram showing an example of a layout of pixels having thestructure shown in FIGS. 1A and 1B;

FIGS. 23A and 23B are diagrams showing examples of the structure of anelectric current source circuit using the threshold value correctingprinciple of the present invention;

FIGS. 24A and 24B are diagrams showing examples of the structure of anelectric current source circuit using the threshold value correctingprinciple of the present invention;

FIGS. 25A and 25B are diagrams showing examples of the structure of anelectric current source circuit using the threshold value correctingprinciple of the present invention; and

FIGS. 26A and 26B are diagrams showing examples of the structure of anelectric current source circuit using the threshold value correctingprinciple of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode 1

Embodiment Mode 1 of the present invention is shown in FIG. 1A.Embodiment Mode 1 has a source signal line 101, a first gate signal line102, a second gate signal line 103, TFTs 104 to 107, capacitor means108, an EL element 109, a reset electric power source line 110, anelectric current supply line 111, and an electric power source line 112.In addition, a storage capacitor means 113 for storing an image signalmay also be formed.

A gate electrode of the TFT 104 is connected to the first gate signalline 102, a first electrode of the TFT 104 is connected to the sourcesignal line 101, and a second electrode of the TFT 104 is connected to afirst electrode of the capacitor means 108. A gate electrode and a firstelectrode of the TFT 105 are connected with each other, and alsoconnected to a second electrode of the capacitor means 108. A secondelectrode of the TFT 105 is connected to the reset electric power sourceline 110. A gate electrode of the TFT 106 is connected to the secondelectrode of the capacitor means 108, and to the gate electrode and thefirst electrode of the TFT 105. A first electrode of the TFT 106 isconnected to the electric current supply line 111, and a secondelectrode of the TFT 106 is connected to a first electrode of the ELelement 109. A second electrode of the EL element 109 is connected tothe electric power source line 112, and has a mutual electric potentialdifference with the electric current supply line 111. A gate electrodeof the TFT 107 is connected to the second gate signal line 103, a firstelectrode of the TFT 107 is connected to the source signal line 101, anda second electrode of the TFT 107 is connected to the gate electrode ofthe TFT 106. When forming the storage capacitor means 113, formation ispossible between the gate electrode of the TFT 106 and a position atwhich a fixed electric potential can be obtained, such as the electriccurrent supply line 111.

FIG. 1B shows the timing at which pulses are input to the first and thesecond gate signal lines. Operation is explained using FIGS. 1A and 1B,and FIGS. 2A to 2D. Note that although a structure is used here whereinthe TFTs 104 and 107 are n-channel TFTs, and the TFTs 105 and 106 arep-channel TFTs, the TFTs 104 and 107 may have any polarity, providedthat they function as simple switching elements.

The electric potential of the reset electric power source line 110 isV_(Resets) and the electric potential of the electric current supplyline 111 is V_(DD), where V_(Reset)<V_(DD). The electric potential ofthe source signal line 101 first becomes V_(SS) (whereV_(SS)<V_(Reset)), and in addition, the second gate signal line 103becomes H level and the TFT 107 turns on. The electric potentials of thegate electrodes of the TFTs 105 and 106 thus drop. The voltage betweenthe gate and the source of the TFT 106 soon becomes less than thethreshold value, and the TFT 106 turns on. The voltage between the gateand the source of the TFT 105 also becomes less than the thresholdvalue, and the TFT 105 also turns on (see FIG. 2A). Although the TFT 104is off in FIG. 2A at this point, it may also be on during this period.

An electric current path develops from the reset electric power sourceline 110 to the TFT 105 to the TFT 107 and to the source signal line 101when the TFT 105 turns on. The second gate signal line 103 thereforebecomes L level after the TFT 105 turns on, and the TFT 107 turns off.The first gate signal line 102 becomes H level at the same time, and theTFT 104 turns on. Electric charge thus moves as shown in FIG. 2B. TheTFT 105 is on, and therefore the electric potentials of the gateelectrodes of the TFTs 105 and 106 increase. The gate and the drain ofthe TFT 105 are connected here, and therefore the TFT 105 turns off atthe point when the voltage between the gate and the source of the TFT105, that is, the voltage between the source and the drain of the TFT105, becomes equal to the threshold value. The electric potentials ofthe gate electrodes of the TFTs 105 and 106 is (V_(Reset)−|V_(th)|) atthis point. In focusing on the capacitor means 108, however, electriccharge accumulates such that the voltage between both electrodes of thecapacitor means 108 becomes (V_(Reset)−|V_(th)|−V_(SS)).

An image signal is then input from the source signal line 101 (see FIG.2C). The electric potential of the source signal line 101 changes byV_(Data) from V_(SS). The electric potentials of the gate electrodes ofthe TFTs 105 and 106 also change by V_(Data) due to capacitive couplingwith the capacitor means 108. The TFT 105 should not turn on at thispoint. Conditions of the values of V_(Data) at this point are discussedbelow. On the other hand, the electric potential of the source of theTFT 106 is V_(DD) (where V_(DD)>V_(Reset)), and the voltage between thegate and the source of the TFT 106 becomes(V_(Reset)−|V_(th)|+V_(Data)−V_(DD)). A drain current corresponding tothe voltage between the gate and the source of the TFT 106 is suppliedto the EL element 109, and light is emitted (see FIG. 2D).

The relationship between the sizes of the electric potential V_(Reset)of the reset electric power source line 110, the electric potentialV_(DD) of the electric current supply line 111, the electric potentialof the source signal line 101, and the image signal V_(Data) isexplained here using FIG. 2E.

First of all, the fixed electric potential size relationship followsV_(SS)<V_(Reset)<V_(DD).

Next, consider the electric potentials of the gate electrodes of theTFTs 105 and 106. The electric potentials of the gate electrodes of theTFTs 105 and 106 become the electric potential shown by symbol [1] inFIG. 2E due to the initialization of FIG. 2A, that is, V_(SS). Theelectric potentials of the gate electrodes of the TFTs 105 and 106 risein the period during which storage of the threshold value is performed,and finally arrive at the electric potential shown by symbol [2] in FIG.2E, that is, (V_(Reset)−|V_(th)|). The electric potentials thenadditionally change by V_(Data) from the potential shown by symbol [2]when the image signal is input. The electric potentials of the gateelectrodes of the TFTs 105 and 106 become lower than the electricpotential of symbol [2] in the case where V_(Data) is a negative value.That is, the voltage between the gate and the source of the TFT 105becomes lower than the threshold value, and the TFT 105 turns on, andthis is contrary to the previous conditions. It is therefore necessaryfor V_(Data) to be a positive value. The electric potentials of the TFTs105 and 106 become electric potentials shown by symbol [3] in FIG. 2Edue to the input image signal, that is, (V_(Reset)−|V_(th)|+V_(Data)).Further, the TFT 106 turns off if the electric potential of the gateelectrode of the TFT 106 becomes higher than V_(DD)−|V_(th)|, andtherefore the range of electric potential values which the image signalV_(Data) is capable of taking is the range denoted by reference numeral200 in FIG. 2E. In other words, it is necessary that the followingrelationship be true: 0≦V_(Data)≦V_(DD)−V_(Reset) (preferably,0<V_(Data)≦V_(DD)−V_(Reset) to ensure that the TFT 105 turns off).However, at a gray scale 0, that is, when the EL element 109 is in astate of absolutely no light emission, an electric potential that isslightly higher than the electric potential at which the TFT 106 turnsoff, in other words, slightly higher than (V_(DD)−V_(Reset)), may beapplied.

The closer V_(Data) comes to zero at this point, the larger the absolutevalue of the voltage between the gate and the source of the TFT 106, andtherefore the higher the brightness of the EL element 109 becomes. Thelarger V_(Data) becomes, the smaller the absolute value of the voltagebetween the gate and the source of the TFT 106 becomes, and thereforethe brightness of the EL element 109 is low.

Display of an image is performed by performing the above operations overone screen. Storage of the threshold value is accomplished in thepresent invention by using only the capacitor means 108, and thereforeit is possible to perform accurate correction of the threshold valuewithout dispersion in the capacitance values influencing the value ofelectric current flowing in the EL elements 109, as discussed above.

Embodiment Mode 2

A digital gray scale method for controlling the EL element 109 in onlytwo states, one having a brightness of 100% and one a brightness of 0%,by using a region in which it is difficult for TFT threshold values andthe like to influence the on electric current is proposed as a methoddiffering from the analog gray scale method discussed above. Only twogray scales, white and black, can be achieved by this method, andtherefore multiple gray scales are realized by combining this methodwith a time gray scale method, a surface area gray scale method, or thelike.

The term time gray scale method refers to a method in which a visiblebrightness difference can be achieved by utilizing a difference in theamount of time that the EL elements 109 emit light. The operation ofthis method will be described in detail in another section of thisspecification, and only two states of the EL elements 109, that is,light emission and non-light emission, need to be used with this type ofdriving method. Therefore only two electric potentials need to beimparted by the image signal V_(Data), that is, H level and L level.

The TFT 106 is a p-channel TFT here, and therefore the EL element 109emits light when V_(Data) is L level, and the EL element 109 does notemit light when V_(Data) is H level. From the conditions of V_(Data)shown in Embodiment Mode 1, the electric potential is in the range shownby the reference numeral 200 in FIG. 2E and as much electric current aspossible can be supplied to the EL element 109 at this point whenV_(Data) is L level. In addition, an electric potential at which the TFT105 does not turn on may also be used. In other words, an electricpotential equal to, or slightly greater than, (V_(Reset)−|V_(th)|) maybe used. On the other hand, an electric potential able to ensure thatthe TFT 106 turns off may be used when V_(Data) is H level. It is notparticularly necessary that the electric potential be in the rangedenoted by the reference numeral 200 for this case. Rather, it isdesirable that an electric potential higher than the range denoted bythe reference numeral 200 (for example, V_(DD) or the like) be input.

Embodiment Mode 3

An example in which some TFT connections differ is shown in FIG. 3A as athird embodiment mode. Although generally similar to the structure shownin FIG. 1A, there is a difference in that a first electrode of a TFT 307is connected to a second electrode of a TFT 304, not to a source signalline.

Operation is explained following FIGS. 3B to 3E. The electric potentialof a reset electric power source line 310 is V_(Reset), and the electricpotential of an electric current supply line 311 is V_(DD), such thatV_(Reset)<V_(DD). First, the electric potential of a source signal line301 becomes V_(SS) (where V_(SS)<V_(Reset)), and in addition, first andsecond gate signal lines 302 and 303 become H level, while TFTs 304 and307 turn on. The electric potentials of gate electrodes of TFTs 305 and306 thus drop. The voltage between the gate and the source of the TFT305 soon becomes lower than the threshold value of the TFT 305, whichturns on, and the voltage between the gate and the source of the TFT 306becomes lower than the threshold value of the TFT 306, which also turnson (see FIG. 3B).

An electric current path from the reset electric power source line 310to the TFT 305, to the TFT 307, to the TFT 304, and to the source signalline 301 develops due to the TFT 305 turning on. The second gate signalline 303 therefore becomes L level immediately after both the TFTs 305and 306 turn on, and the TFT 307 turns off. Movement of electric chargeas shown in FIG. 3C thus develops. The TFT 305 is on, and therefore theelectric potentials of the gate electrodes of the TFTs 305 and 306 rise.The gate and the drain of the TFT 305 are connected here, and thereforethe TFT 305 turns off at the point when the voltage between the gate andthe source of the TFT 305, that is the voltage between the source andthe drain of the TFT 305, becomes equal to the threshold value V_(th).The electric potentials of the gate electrodes of the TFTs 305 and 306are (V_(Reset)−|V_(th)|) at this point. In focusing on the capacitormeans 308, however, electric charge accumulates by the amount that theelectric potential of the second electrode changes.

An image signal is then input from the source signal line 301 (see FIG.3D). The electric potential of the source signal line 301 changes byV_(Data) from V_(SS). The electric potentials of the gate electrodes ofthe TFTs 305 and 306 also change by V_(Data) due to capacitive couplingwith the capacitor means 308. The TFT 305 does not turn on at thispoint. On the other hand, the electric potential of the source of theTFT 306 is V_(DD) (where V_(DD)>V_(Reset)), and the voltage between thegate and the source of the TFT 306 becomes(V_(Reset)−|V_(th)+V_(Data)−V_(DD)). A drain current corresponding tothe voltage between the gate and the source of the TFT 306 is suppliedto the EL element 309, and light is emitted (see FIG. 3E).

Embodiment Mode 4

A method of combining a digital gray scale method and a time gray scalemethod is explained here. The structure of a pixel shown in FIG. 9A isan example that can be employed by driving with using this type ofmethod. It becomes possible to minutely control the length of timeduring which light is emitted by using an erasure TFT 906 in addition toa switching TFT 904, and a driver TFT 905.

One frame period is divided into a plurality of subframe periods whencombining a digital gray scale method and a time gray scale method, asshown in FIG. 9B. Each of the subframe periods has an address (write in)period and a sustain (light emitting) period as shown in FIG. 9C, and inaddition, an erasure period if necessary. A method of gray scaleexpression may be used, for example, in which the number of subframeperiods are formed corresponding to the number of display bits, and thelengths of the sustain (light emitting) period in each of the subframeperiods are taken as 2^((n-1)):2^((n-2)): . . . :2:1. Light emission ornon-light emission by the EL element is selected for each sustain (lightemitting) period, and gray scale expression is performed by utilizingthe difference in the lengths of the total time during which the ELelement emits light in one frame period. It is recognized thatbrightness increases with a longer total light emitting period, andbrightness decreases with a shorter total light emitting period. A 4-bitgray scale example is shown in FIG. 9B, and one frame period is dividedinto four subframe periods. By combining the subframe periods withsustain (light emitting) periods, 2⁴=16 gray scales can be expressed.Note that the number of divisions of the frame period is not limited tofour, and that it is also possible to further divide the frame periodinto more subframe periods.

Further, it is not always necessary that the relative lengths of thesustain (light emitting) periods during gray scale expression be2^((n-1)):2^((n-2)): . . . :2:1.

The length of the sustain (light emitting) period of lower bits becomesvery short when forming multiple gray scales by this method, andtherefore a period develops, after the sustain (light emitting) periodis complete and the next address period immediately begins, during whichaddress (write in) periods of different subframe periods overlap. Inthis case, an image signal input to a certain pixel is also input at thesame time to different pixels, and correct display therefore cannot beperformed. The erasure period is formed in order to solve this problem,and is formed after Ts3 and Ts4 in FIG. 9B so that address (write in)periods belonging to adjacent subframe periods do not overlap. Erasureperiods are not formed in SF1 and SF2, which have long sustain (lightemitting) periods and in which there is no concern that address (writein) periods belonging to adjacent subframe periods will overlap.

FIG. 4A shows a method of combining a digital gray scale method and atime gray scale method, wherein a third gate signal line 414 and anerasure TFT 415 are added to the pixel structure shown in EmbodimentMode 1. A gate electrode of the erasure TFT 415 is connected to thethird gate signal line 414, a first electrode of the erasure TFT 415 isconnected to a gate signal line of a TFT 406, and a second electrode ofthe erasure TFT 415 is connected to an electric current supply line 411.Further, in the case where a storage capacitor means 413 for storing animage signal is formed, it may be formed between a gate electrode of theTFT 406 and a location at which a fixed electric potential can beobtained. The storage capacitor means 413 is formed between the gateelectrode of the TFT 406 and the electric current supply line 411 inFIGS. 4A to 4C, but it may also be formed, for example, between the gateelectrode of the TFT 406 and a prior stage gate signal line. Further, itmay also be formed between a second electrode of the TFT 404 and a fixedelectric potential such as the electric current supply line 411, and itmay be formed on both if there is a desire to make the storagecapacitance larger.

Operations from initialization, to input of an image signal, and tolight emission is similar to the explanation provided in EmbodimentMode 1. Note that the erasure TFT 415 is off during initialization,input of the image signal, and the sustain (light emitting) period.

Operation from the sustain (light emitting) period to the erasure periodis explained here using FIGS. 4A to 4C, and FIGS. 12A to 12C. FIG. 12Ais similar to the diagram shown in FIG. 9B, and one frame period hasfour subframe periods. Subframe periods SF3 and SF4, which have shortsustain (light emitting) periods, each have erasure periods Te3 and Te4,as shown in FIG. 12B. Operation during the sustain period SF3 is takenas an example here for explanation.

Electric current corresponding to the voltage between the gate and thesource of the TFT 406 flows in the EL element 409 as shown in FIG. 4Bafter input of the image signal is complete. A pulse is then input tothe third gate signal line 414 when a timing for completion of thecorresponding sustain (light emitting) period is complete, the thirdgate signal line 416 becomes H level, and the TFT 415 turns on. Thevoltage between the gate and the source of the TFT 406 is zero, as shownin FIG. 4C. The TFT 406 thus turns off by this operation, and electriccurrent to the EL element 409 is cut off. The EL element 409 istherefore forcibly placed in a non-light emitting state.

The timing chart for these operations is shown in FIG. 12C. Periods forperforming initialization, threshold value storage, and write in of theimage signal are contained in the address (write in) period. A periodbeginning after a pulse is input to the third gate signal line 414 afterthe sustain (light emitting) period and the EL element 409 becomesnon-light emitting, up through when a pulse is next input to the secondgate signal line 403 and initialization begins, is the erasure period.

Embodiment Mode 5

An example of performing erasure operations using a structure thatdiffers from the structure of Embodiment Mode 4 is explained using FIGS.5A to 5C in Embodiment Mode 5.

FIG. 5A shows a structure having the erasure TFT 415, similar toEmbodiment Mode 4. However, although the first electrode of the TFT 415is connected to the gate electrode of the TFT 406, namely to a secondelectrode of capacitor means 408 in Embodiment Mode 4, the firstelectrode of the TFT 415 is connected to a first electrode of thecapacitor means 408 in FIG. 5.

Electric current corresponding to the voltage between the gate and thesource of the TFT 406 flows in the EL element 409 as shown in FIG. 5Bafter input of the image signal is complete. A pulse is then input tothe third gate signal line 414, which becomes H level, when a timing forcompletion of the corresponding sustain (light emitting) period isreached, and the TFT 415 turns on. The electric potential of the firstelectrode of the capacitor means 408 becomes V_(DD), as shown in FIG.5C. The electric potential of the gate electrode of the TFT 406consequently becomes higher than V_(DD), and therefore the voltagebetween the gate and the source becomes a positive value. The TFT 406thus turns off by this operation, electric current to the EL element 409is cut off, and the EL element 409 is forcibly placed in a non-lightemitting state.

Operations during the erasure period are such that electric current tothe EL element 409 is cut off by making the voltage between the gate andthe source of the TFT 406, which functions as a driver TFT in order tosupply electric current to the EL element 409, a voltage at which theTFT 406 turns off. Provided that operation is based upon this principle,there are no limitations placed on the placement of the erasure TFT 415.

Embodiment Mode 6

Operation during the erasure period in Embodiment Modes 4 and 5 is suchthat electric current to the EL element 409 is cut off by making thevoltage between the gate and the source of the TFT 406, which functionsas a driver TFT for supplying electric current to the EL element 409, avoltage at which the TFT 406 turns off. An example of using anothermethod is shown in FIG. 6A. The erasure TFT 415 is formed between theelectric current supply line 411 and the gate electrode of the TFT 406,or between the electric current supply line 411 and the first electrodeof the capacitor means 408 in Embodiment Modes 4 and 5. However, theerasure TFT 415 is formed between the TFT 406 and the EL element 409 inEmbodiment Mode 6. That is, a TFT is added in any place of the pathwayfrom the electric current supply line to the TFT 406 and to the ELelement 409 with the method of Embodiment Mode 6, and the supply ofelectric current to the EL element 409 is cut off by turning this TFToff.

Initialization, input of an image signal, and light emission are similarto those of Embodiment Modes 4 and 5. However, the erasure TFT 415 is ononly during the sustain (light emitting) period, and electric currentflows as shown in FIG. 6B. The TFT 415 is off during initialization,input of the image signal, and during the erasure period, and electriccurrent to the EL element 409 is cut off during these periods.

Differences in operation between Embodiment Mode 6 and Embodiment Modes4 and 5 are explained. The voltage between the gate and the source ofthe TFT 406 is controlled by turning the erasure TFT 415 on once inEmbodiment Modes 4 and 5, and therefore the EL element 409 does not emitlight after this operation is performed until the next image signal iswritten in. Consequently, pulses input to the third gate signal line 414may be short pulses input at a timing at which the erasure periodbegins, as shown in FIG. 12C. In Embodiment Mode 6, however, it isnecessary for the erasure TFT 415 to be on throughout the sustain (lightemitting) period, and therefore it is necessary to input pulses to thethird gate signal line 415, the pulses lengths equal to the sustain(light emitting) periods, for each of the subframe periods.

Further, although the erasure TFT 415 uses an n-channel TFT inEmbodiment Modes 4, 5, and 6, there are no particular limitations placedon the polarity in Embodiment Mode 6 because the erasure TFT 415functions solely as a switching element.

Embodiment Mode 7

Initialization operations prior to the input of image signals areperformed by using a certain TFT in Embodiment Modes 1 to 6.Specifically, a threshold value appearing between the source and thedrain of a TFT, which has a connection between a gate electrode and adrain electrode, is obtained. In contrast, a diode 713 is used as asubstitute for the TFT in FIG. 7A. A first electrode of the diode 713 isconnected to a gate electrode of a TFT 706, and a second electrode ofthe diode 713 is connected to a second gate signal line 703. Further, ifcapacitor means 712 is formed in order to store image signals, then thecapacitor means may be formed between the gate electrode of the TFT 706and a location at which a fixed electric potential can be obtained, suchas an electric current supply line 710. Furthermore, the capacitor means712 may also be formed between a second electrode of a TFT 704 and alocation at which a fixed electric potential can be obtained, such asthe electric current supply line 710. The capacitor means may also beformed in both locations if a large value of storage capacitance isdesired. Reference numerals 701, 707, 709 and 711 denote a source signalline, a capacitor means, a reset power source line and a power supplyline, respectively.

Only operations during initialization differ from Embodiment Mode 1.Explanations regarding input of an image signal and light emittingoperations are omitted here. Operations during initialization areexplained using FIG. 7B.

First, the electric potential of the second gate signal line 703 is setto H level (for example, V_(DD)). A forward bias is then imparted to thediode 713 if the electric potential of the second gate signal line 703is set to L level (for example, V_(SS)) at the initialization timing.Electric current develops as shown in FIG. 7B from nodes having a highelectric potential to nodes having a low electric potential, and theelectric potential of a gate electrode of a TFT 705, and the electricpotential of the gate electrode of the TFT 706, drop The voltage betweenthe gate and the source of the TFT 705 soon becomes lower than thethreshold voltage, and the TFT 705 turns on. Thereafter, the voltagebetween the gate and the source of the TFT 706 becomes lower than thethreshold voltage, and the TFT 706 also turns on. Initialization iscomplete at this point, and the electric potential of the second gatesignal line 703 once again becomes H level. A reverse bias is impartedto the diode 713 at this point, and electric current does not flowduring periods for performing image signal input and light emissionoperations.

Electric current corresponding to the input image signal then flows inthe EL element 708, and the EL element 708 emits light, similar toEmbodiment Mode 1.

FIG. 7C shows an example of forming capacitor means 714 as a substitutefor the diode 713. A first electrode of the capacitor means 714 isconnected to the gate electrode of the TFT 706, and a second electrodeof the capacitor means 714 is connected to the second gate signal line703. Also in this case, operation is similar to that shown in FIG. 7B.First, the second gate signal line 703 is set to H level, and theelectric potential of the second gate signal line 703 is set to L levelat the initialization timing. The TFT 705 turns off at this point, andtherefore the electric potentials of the gate electrodes of the TFTs 705and 706 drop due to capacitive coupling with the capacitor means 714.The voltage between the gate and the source of the TFT 705 soon becomeslower than the threshold voltage, and the TFT 705 turns on. The voltagebetween the gate and the source of the TFT 706 then becomes lower thanthe threshold voltage, and the TFT 706 also turns on.

The TFT 704 then turns on, and input of an image signal is performed.The second gate signal line 703 is L level at this point, but may alsobe set to H level during input of the image signal.

Electric current corresponding to the input image signal then flows inthe EL element 708, and the EL element 708 emits light, similar toEmbodiment Mode 1.

Embodiment Mode 8

Display devices having an integrally formed pixel portion and peripheralcircuits, formed by TFTs and the like built into a substrate, have theadvantages of small size and light weight. However, their manufacturingprocesses are complex, such as element formation by repeatedlyperforming film formation and etching, and the addition of impurityelements for imparting conductivity to semiconductor layers. Inparticular, processes for adding impurity elements differ betweenp-channel TFTs and n-channel TFTs, and this therefore invites furtherincreases of processing.

Processes for adding impurity elements can be partly omitted bystructuring the pixel portion and the peripheral circuits using TFTshaving a single polarity. Not only does it thus become possible toshorten processing, but the number of photomasks can also be reduced.

An example of a structure that uses TFTs having a single polarity typeis the structure disclosed in Japanese Patent Application No.2001-348032 by the applicants of the present invention. This is astructure in which only n-channel TFTs having a high field-effectmobility are used, and in addition, a structure in which drops inbrightness do not easily occur, even if EL elements deteriorate.

A structure provided with both advantages, that is a structure in whichdrops in brightness following deterioration of EL elements arecontrolled, and one in which correction of dispersion in TFT thresholdvalues is possible, is explained in Embodiment Mode 8 by combining theaforementioned technique with the present invention.

FIG. 16A shows an example structure. The structure has a source signalline 1601, a first gate signal line 1602, a second gate signal line1603, a third gate signal line 1604, TFTs 1605 to 1609, capacitor means1610 and 1611, an EL element 1612, a reset electric power source line1613, an electric current supply line 1614, and electric power sourcelines 1615 and 1616. If a storage capacitor means 1617 is formed, it maybe formed between a gate electrode of the TFT 1607 and a location atwhich a fixed electric potential can be obtained, such as the electriccurrent supply line 1614.

A gate electrode of the TFT 1605 is connected to the first gate signalline 1602, a first electrode of the TFT 1605 is connected to the sourcesignal line 1601, and a second electrode of the TFT 1605 is connected toa first electrode of the capacitor means 1610. A gate electrode and afirst electrode of the TFT 1606 are connected with each other, and thenconnected to a second electrode of the capacitor means 1610. A secondelectrode of the TFT 1606 is connected to the reset electric powersource line 1613. The gate electrode of the TFT 1607 is connected to thegate electrode and the first electrode of the TFT 1606. A firstelectrode of the TFT 1607 is connected to the electric current supplyline 1614, and a second electrode of the TFT 1607 is connected to afirst electrode (anode) of the EL element 1612. A gate electrode of theTFT 1608 is connected to the second gate signal line 1603, a firstelectrode of the TFT 1608 is connected to the source signal line 1601,and a second electrode of the TFT 1608 is connected to the gateelectrodes of the TFTs 1606 and 1607. A gate electrode of the TFT 1609is connected to the third gate signal line 1604, a first electrode ofthe TFT 1609 is connected to the electric power source line 1616, and asecond electrode of the TFT 1609 is connected to the first electrode(anode) of the EL element 1612. A second electrode (cathode) of the ELelement 1612 is connected to the electric power source line 1615. Afirst electrode of the capacitor means 1611 is connected to the secondelectrode of the TFT 1605, and a second electrode of the capacitor means1611 is connected to the first electrode (anode) of the EL element 1612.

Operation is explained following FIG. 16B and FIGS. 17A to 17E. A timingchart for pulses input into the first to the third gate signal lines1602 to 1604, and for an image signal input to the source signal line1601 is shown in FIG. 16B. The image signal is input at a timing denotedby symbol “V”, and at a predetermined electric potential.

The electric potential of the reset electric power source line 1613 isV_(Reset), the electric potential of the electric current supply line1614 is V_(DD), the electric potential of the electric power source line1615 is V_(C), and the electric potential of the electric power sourceline 1616 is V_(SS), where V_(SS)<V_(C)<V_(DD)<V_(Reset). First, theelectric potential of the source signal line 1601 is set to V_(x) (whereV_(x)>V_(Reset)). The second gate signal line 1603 and the third gatesignal line 1604 then become H level, the TFTs 1608 and 1609 both turnon, an electric current develops as shown in FIG. 17A, and the electricpotentials of the gate electrodes of the TFTs 1606 and 1607 rise. Thevoltage between the gate and the source of the TFT 1606 soon rises abovethe threshold value, and the TFT 1606 turns on. In addition, the voltagebetween the gate and the source of the TFT 1607 rises above thethreshold value, and the TFT 1607 turns on. Initialization is thuscomplete by the above operations.

The second gate signal line becomes L level immediately afterinitialization is complete, and the TFT 1608 turns off. The electricpotentials of the gate electrodes of the TFTs 1606 and 1607 thus beginto drop. The TFT 1606 turns off at the point where the electricpotential becomes (V_(Reset)+V_(th)), that is when the voltage betweenthe gate and the source of the TFT 1606 becomes equal to the thresholdvalue. An electric potential difference thus develops between bothelectrodes of the capacitor means 1610, and this electric potentialdifference is stored.

On the other hand, the voltage between the gate and the source of theTFT 1607 at this point exceeds the threshold value, and therefore theTFT 1607 turns on. The TFT 1609 also turns on, and therefore electriccurrent flows as shown in FIG. 17B in a pathway from the electriccurrent supply line 1614, to the TFT 1607, to the TFT 1609, and to theelectric power source line 1616. Electric current does not flow in theEL element 1612 at this point, however, because V_(SS)<V_(C). The ELelement 1612 therefore does not emit light.

Input of an image signal begins next. An image signal having apredetermined electric potential is input to the source signal line1601, which is fixed to the electric potential V_(x), and the electricpotential of the source signal line 1601 becomes (V_(x)−V_(Data)). Thevoltage between the gate and the source of the TFT 1606 becomes lowerthan the threshold value, and the TFT remains off. On the other hand,the voltage between the gate and the source of the TFT 1607 becomes(V_(Reset)+V_(th)−V_(Data)−V_(DD)), and a drain current corresponding tothis voltage flows (see FIG. 17C).

The first gate signal line 1602 becomes L level when input of the imagesignal is complete, and the TFT 1605 turns off. The third gate signalline 1604 then becomes L level, and the TFT 1609 turns off. Electriccurrent flowing in the TFT 1607 thus flows in the EL element 1612, andlight is emitted (see FIG. 17D).

An explanation regarding the relationship between the sizes of theelectric potential V_(Reset) of the reset electric power source line1613, the electric potential V_(DD) of the electric current supply line1614, the electric potential of the source signal line 1601, and theimage signal V_(Data) is made here using FIG. 17E.

Consider the electric potentials of the gate electrodes of the TFTs 1606and 1607. The electric potentials of the gate electrodes of the TFTs1606 and 1607 become the electric potential denoted by symbol [1] inFIG. 17E due to the initialization of FIG. 17A. That is, the electricpotentials become V_(x). The electric potentials of the gate electrodesof the TFTs 1606 and 1607 drop during a period for performing storage ofthe threshold values, and finally become the electric potential denotedby symbol [2] in FIG. 17E. That is, the electric potentials become(V_(Reset)+|V_(th)|). Subsequently, when an image signal is input, theelectric potentials of the gate electrodes of the TFTs 1606 and 1607further change by V_(Data) from the electric potential of symbol [2].The electric potentials of the gate electrodes of the TFTs 1606 and 1607becomes higher than the electric potential of symbol [2] here in thecase where the change is positive. That is, the voltage between the gateand the source of the TFT 1606 becomes higher than the thresholdvoltage, and the TFT 1606 turns on, which is contrary to the priorconditions. It is therefore necessary that the change to the imagesignal be negative. The electric potentials of the TFTs 1606 and 1607therefore become an electric potential denoted by symbol [3] in FIG. 17Edue to the input of the image signal. That is, the electric potentialsbecome (V_(Rese)t+|V_(th)|−V_(Data)). Further, the electric potential ofthe gate electrode of the TFT 1607 becomes lower than VDD+|V_(th)|, andthe TFT 1607 turns off, and therefore a range of electric potentials atwhich the image signal can be obtained is a range denoted by referencenumeral 1700 in FIG. 17E. That is, it is necessary that0≦V_(Data)≦V_(Reset)−V_(DD) (preferably 0<V_(Data)≦V_(Reset)−V_(DD) inorder to ensure that the TFT 1606 is off). However, at a gray scale ofzero, namely when the EL element 1612 is in a non-light emitting state,an electric potential slightly larger than (V_(Reset)−V_(DD)) may alsobe imparted as V_(Data) so as to ensure that the TFT 1607 turns off.

The closer V_(Data) is to zero at this point, the higher the absolutevalue of the voltage between the gate and the source of the TFT 1607becomes, and therefore the higher the brightness of the EL element 1612becomes. The larger V_(Data) becomes, the smaller the absolute value ofthe voltage between the gate and the source of the TFT 1607, andtherefore the lower the brightness of the EL element 1612 becomes.

The above explanation is made for an example of performing display by ananalog gray scale method, but display by a digital gray scale methodlike that disclosed by Embodiment Mode 2 can also be similarly made.Further, it is easy to combine Embodiment Mode 8 with a structure inwhich an erasure TFT is formed when using a time gray scale method.

EMBODIMENTS

Hereafter, the embodiments of the invention will be described.

Embodiment 1

In this embodiment, the configuration of a light-emitting device inwhich analog video signals are used for video signals for display willbe described. A configuration example of the light-emitting device isshown in FIG. 18A. The device has a pixel portion 1802 wherein aplurality of pixels is arranged in a matrix shape over a substrate 1801,and it has a source signal line driver circuit 1803 and first and secondgate signal line driver circuits 1804 and 1805 around the pixel portion.In FIG. 18A, two couples of gate signal line driver circuits are used,which control first and second gate signal lines.

Signals inputted to the source signal line driver circuit 1803, and thefirst and second gate signal line driver circuits 1804 and 1805 areprovided from outside through a flexible printed circuit (FPC) 1806.

FIG. 18B shows a configuration example of the source signal line drivercircuit. This is the source signal line driver circuit for using analogvideo signals for video signals for display, which has a shift register1811, a buffer 1812, and a sampling circuit 1813. Not shownparticularly, but a level shifter may be added if necessary.

The operation of the source signal line driver circuit will bedescribed. FIG. 19A shows the more detailed configuration, thusreferring to the drawing.

A shift register 1901 is formed of a plurality of flip-flop circuits(FF) 1902, to which the clock signal (S-CLK), the clock inverted signal(S-CLKb), and the start pulse (S-SP) are inputted. In response to thetiming of these signals, sampling pulses are outputted sequentially.

The sampling pulses outputted from the shift register 1901 are passedthrough a buffer 1903 etc. and amplified, and then inputted to asampling circuit. The sampling circuit 1904 is formed of a plurality ofsampling switches (SW) 1905, which samples video signals in a certaincolumn in accordance with the timing of inputting the sampling pulses.More specifically, when the sampling pulses are inputted to the samplingswitches, the sampling switches 1905 are turned on. The potential heldby the video signals at this time is outputted to the respective sourcesignal lines through the sampling switches.

Subsequently, the operation of the gate signal line driver circuit willbe described. FIG. 19B shows the more detailed configuration of thefirst and second gate signal line driver circuits 1804 and 1805 shown inFIG. 18C. The first gate signal line driver circuit has a shift registercircuit 1911, and a buffer 1912, which is driven in response to theclock signal (G-CLK1), the clock inverted signal (G-CLKb1), and thestart pulse (G-SP1). The second gate signal line driver circuit 2405 mayhave a same configuration.

The operation from the shift register to the buffer is the same as thatin the source signal line driver circuit. The selecting pulses amplifiedby the buffer select respective gate signal lines for them. The firstgate signal line driver circuit sequentially selects first gate signallines G₁₁, G₂₁, . . . and G_(m1), and the second gate signal line drivercircuit sequentially selects second gate signal lines G₁₂, G₂₂, andG_(m2). A third gate signal line driver circuit, not shown, is also thesame as the first and second gate signal line driver circuits,sequentially selecting third gate signal lines G₁₃, G₂₃, . . . andG_(m3). In the selected row, video signals are written in the pixel toemit light according to the procedures described in the embodiment mode.

Note that, as one example of the shift register that formed of aplurality of D-flip-flops is shown here. However, such the configurationis acceptable that signal lines can be selected by a decoder and thelike.

Embodiment 2

In this embodiment, a configuration of a light-emitting device in whichdigital video signals are used for video signals for display will bedescribed. FIG. 20A shows a configuration example of the light-emittingdevice. The device has a pixel portion 2002 wherein a plurality ofpixels is arranged in a matrix shape over a substrate 2001, and it has asource signal line driver circuit 2003, and first and second gate signalline driver circuits 2004 and 2005 around the pixel portion. In FIG.20A, two couples of gate signal line driver circuits are used, whichcontrol first and second gate signal lines.

Signals inputted to the source signal line driver circuit 2003, and thefirst and fourth gate signal line driver circuits 2004 and 2005 aresupplied from outside through a flexible printed circuit (FPC) 2006.

FIG. 20B shows a configuration example of the source signal line drivercircuit. This is the source signal line driver circuit for using digitalvideo signals for video signals for display, which has a shift register2011, a first latch circuit 2012, a second latch circuit 2013, and a D/Aconverter circuit 2014. Not shown in the drawing particularly, but alevel shifter may be added if necessary.

The first and second gate signal line driver circuits 2004 and 2005 canbe same as those shown in Embodiment 1, thus omitting the illustrationand description here.

The operation of the source signal line driver circuit will bedescribed. FIG. 21A shows the more detailed configuration, thusreferring to the drawing.

A shift register 2101 is formed of a plurality of flip-flop circuits(FF) 2110 or the like, to which the clock signal (S-CLK), the clockinverted signal (S-CLKb), and the start pulse (S-SP) are inputted.Sampling pulses are sequentially outputted in response to the timing ofthese signals.

The sampling pulses outputted from the shift register 2101 are inputtedto first latch circuits 2102. Digital video signals are being inputtedto the first latch circuits 2102. The digital video signals are held ateach stage in response to the timing of inputting the sampling pulses.Here, the digital video signals are inputted by three bits. The videosignals at each bit are held in the respective first latch circuits.Here, three first latch circuits are operated in parallel by onesampling pulse.

When the first latch circuits 2102 finish to hold the digital videosignals up to the last stage, latch pulses are inputted to second latchcircuits 2103 during the horizontal retrace period, and the digitalvideo signals held in the first latch circuits 2102 are transferred tothe second latch circuits 2103 all at once. After that, the digitalvideo signals held in the second latch circuits 2103 for one row areinputted to D/A converter circuits 2104 simultaneously.

While the digital video signals held in the second latch circuits 2103are being inputted to D/A converter circuits 2104, the shift register2101 again outputs sampling pulses. Subsequent to this, the operation isrepeated to process the video signals for one frame.

The D/A converter circuits 2104 convert the inputted digital videosignals from digital to analog and output them to the source signallines as the video signals having the analog voltage.

The operation described above is conducted throughout the stages duringone horizontal period. Accordingly, the video signals are outputted tothe entire source signal lines.

Note that, as described in the Embodiment 1, such the configuration isacceptable that a decoder or the like is used instead of the shiftregister to select signal lines.

Embodiment 3

In Embodiment 2, the digital video signal is subjected todigital-to-analog conversion by the D/A converting circuit and writteninto the pixel. The light-emitting device of the present invention canalso conduct gradation representation by a time gradation method. Inthis case, as shown in FIG. 21B, the D/A converting circuit is notrequired and the gradation representation is controlled according to alength of a light emitting time of the EL element. Thus, it isunnecessary to parallel-process video signals of respective bits so thatthe first and second latch circuits each may also have one bit. At thistime, with respect to the digital video signal, each bit is seriallyinputted, held in succession in the latch circuit, and written into thepixel. Of course, the latch circuit of the required number of bits maybe provided in parallel.

Embodiment 4

In this embodiment, an example in which a light-emitting device ismanufactured according to the present invention will be described usingFIGS. 15A to 15C.

FIG. 15A is a top view of a light-emitting device produced by sealing anelement substrate in which TFTs are formed with a sealing member. FIG.15B is a cross sectional view along a line A-A′ in FIG. 15A. FIG. 15C isa cross sectional view along a line B-B′ in FIG. 15A.

A seal member 4009 is provided to surround a pixel portion 4002, asource signal line driver circuit 4003, and first and second gate signalline driver circuits 4004 a and 4004 b which are provided on a substrate4001. In addition, a sealing member 4008 is provided over the pixelportion 4002, the source signal line driver circuit 4003, and the firstand second gate signal line driver circuits 4004 a and 4004 b. Thus, thepixel portion 4002, the source signal line driver circuit 4003, and thefirst and second gate signal line driver circuits 4004 a and 4004 b aresealed with the substrate 4001, the seal member 4009 and the sealingmember 4008 and filled with a filling agent 4210.

Also, the pixel portion 4002, the source signal line driver circuit4003, and the first and second gate signal line driver circuits 4004 aand 4004 b which are provided on the substrate 4001 each have aplurality of TFTs. In FIG. 15B, TFTs (note that an N-channel TFT and aP-channel TFT are shown here) 4201 included in the source signal linedriver circuit 4003 and a TFT 4202 included in the pixel portion 4002,which are formed on a base film 4010 are typically shown.

An interlayer insulating film (planarization film) 4301 is formed on theTFTs 4201 and 4202, and a pixel electrode (anode) 4203 electricallyconnected with the drain of the TFT 4202 is formed thereon. Atransparent conductive film having a large work function is used as thepixel electrode 4203. A compound of indium oxide and tin oxide, acompound of indium oxide and zinc oxide, zinc oxide, tin oxide, orindium oxide can be used for the transparent conductive film. Inaddition, the transparent conductive film to which gallium is added maybe used.

An insulating film 4302 is formed on the pixel electrode 4203. Anopening portion is formed in the insulating film 4302 on the pixelelectrode 4203. In the opening portion, an organic light-emitting layer4204 is formed on the pixel electrode 4203. An organic light emittingmaterial or an inorganic light emitting material that is known can beused as the organic light-emitting layer 4204. In addition, the organiclight emitting material includes a low molecular weight based (monomersystem) material and a high molecular weight based (polymer system)material, and any material may be used.

An evaporation technique or an applying method technique that is knownis preferably used as a method of forming the organic light-emittinglayer 4204. In addition, a laminate structure or a single layerstructure which is obtained by freely combining a hole injection layer,a hole transporting layer, a light emitting layer, an electrontransporting layer, and an electron injection layer is preferably usedas the structure of the organic light emitting layer.

A cathode 4205 made from a conductive film having a light shieldingproperty (typically, a conductive film containing mainly aluminum,copper, or silver, or a laminate film of the conductive film and anotherconductive film) is formed on the organic light emitting layer 4204. Inaddition, it is desirable that moisture and oxygen that exist in aninterface between the cathode 4205 and the organic light-emitting layer4204 are minimized. Thus, a devise is required in which the organiclight emitting layer 4204 is formed in a nitrogen atmosphere or a nobleatmosphere and the cathode 4205 without being exposed to oxygen andmoisture is formed. In this embodiment, the above film formation ispossible by using a multi-chamber type (cluster tool type) filmformation apparatus. A predetermined voltage is supplied to the cathode4205.

By the above steps, a light-emitting element 4303 composed of the pixelelectrode (anode) 4203, the organic light emitting layer 4204, and thecathode 4205 is formed. A protective film 4209 is formed on theinsulating film 4302 so as to cover the light-emitting element 4303. Theprotective film 4209 is effective to prevent oxygen, moisture, and thelike from penetrating the light-emitting element 4303.

Reference numeral 4005 a denotes a lead wiring connected with a powersource, which is connected with a first electrode of the TFT 4202. Thelead wiring 4005 a is passed between the seal member 4009 and thesubstrate 4001 and electrically connected with an FPC wiring 4301 of anFPC 4006 through an anisotropic conductive film 4300.

A glass material, a metallic member (typically, a stainless member), aceramic member, a plastic member (including a plastic film) can be usedas the sealing member 4008. An FRP (fiberglass reinforced plastic)plate, a PVF (polyvinyl fluoride) film, a Mylar film, a polyester film,or an acrylic resin film can be used as the plastic member. In addition,a sheet having a structure in which aluminum foil is sandwiched by a PVFfilm and a Mylar film can be used.

Note that, it is required that the cover member is transparent to thelight when the light generated at the light-emitting element is emittedthrough a cover member side. In this case, a transparent material suchas a glass plate, a plastic plate, a polyester film, or acrylic film isused.

Also, in addition to an inert gas such as nitrogen or argon, ultravioletcurable resin or thermal curable resin can be used for the filling agent4103. PVC (polyvinyl chloride), acrylic, polyimide, epoxy resin, siliconresin, PVB (polyvinyl butyral), or EVA (ethylene vinyl acetate) can beused. In this embodiment, nitrogen is used for the filling agent.

Also, in order to expose the filling agent 4103 to a hygroscopicmaterial (preferably barium oxide) or a material capable of absorbingoxygen, a concave portion 4007 is provided to the surface of the sealingmember 4008 in the substrate 4001 side, and the hygroscopic material orthe material capable of absorbing oxygen which is indicated by 4207 islocated. In order to prevent the material 4207 having a hygroscopicproperty or being capable of absorbing oxygen from flying off, thematerial 4207 having a hygroscopic property or being capable ofabsorbing oxygen is held in the concave portion 4007 by a concave covermember 4208. Note that concave cover member 4208 is formed in a finemeshed shape and constructed such that it transmits air and moisture butdoes not transmit the material 4207 having a hygroscopic property orbeing capable of absorbing oxygen. When the material 4207 having ahygroscopic property or being capable of absorbing oxygen is provided,the deterioration of the light-emitting element 4303 can be suppressed.

As shown in FIG. 15C, a conductive film 4203 a is formed on the leadwiring 4005 a such that it is in contact with the lead wiring 4005 asimultaneously with the formation of the pixel electrode 4203.

Also, the anisotropic conductive film 4300 has a conductive filler 4300a. When the substrate 4001 and the FPC 4006 are bonded to each other bythermal compression, the conductive film 4203 a located over thesubstrate 4001 and the FPC wiring 4301 located on the FPC 4006 areelectrically connected with each other through the conductive filler4300 a.

Embodiment 5

An example of manufacturing pixels actually by using the configurationshown in FIG. 1A is demonstrated with reference to FIG. 22. A portionsurrounded by a dotted line frame 2200 represents one pixel. Anotherfigure numbers are the same as those assigned in FIG. 1A.

A source signal line 101, a reset power source line 110, and a currentsupply line 111 are formed by using a same layer material for forming agate electrode. First and second gate signal lines 102 and 103 areformed by using a wiring material.

The pixel electrode 120 serves as a transparent electrode here, andconnects to a drain electrode of TFT 106. The pixel electrode 120 andthe drain electrode of TFT 106 contact each other without through acontact hole by means of overlapping directly a transparent conductivefilm forming a pixel electrode 120 and wiring materials. Of course,another method may be used to contact the drain electrode of TFT 106 andthe pixel electrode 120.

Though a capacity device 108 and a retention capacity device 113 areformed at between the gate materials and the wiring materials, it is notespecially limited to this type. For ease of illustration, a channellength L and a channel width W of TFTs 104 to 107 are not illustrated asto correspond to the actual sizes. It is possible that the desired sizeof L and W is determined at the designing phase and that each TFTdiffers in size.

Embodiment 6

A light-emitting device using a light-emitting element is a self lightemission type. Thus, such a light-emitting device has high visibility ina light place and a wide viewing angle, as compared with a liquidcrystal display. Therefore, it can be used for a display portion ofvarious electronic apparatuses.

As electronic apparatuses using the light-emitting device of the presentinvention, there are a video camera, a digital camera, a goggle typedisplay (head mount display), a navigation system, a sound reproducingdevice (car audio system, audio component system, or the like), a laptopcomputer, a game machine, a portable information terminal (mobilecomputer, mobile telephone, portable game machine, an electric book, orthe like), an image reproducing device including a recording medium(specifically, apparatus for reproducing an image from a recordingmedium such as a digital versatile disc (DVD), which includes a displaycapable of displaying the image), and the like. In particular, in thecase of the portable information terminal in which a screen is viewedfrom an oblique direction in many cases, it is important that a viewangle is large. Thus, it is desirable that the light-emitting device isused. Concrete examples of those electronic apparatuses are shown inFIGS. 13A to 13H.

FIG. 13A shows a light emitting element display device which includes acabinet 3001, a support base 3002, a display portion 3003, a speakerportion 3004, and a video input terminal 3005. The light-emitting deviceof the present invention can be used for the display portion 3003. Thelight-emitting device is a self light emission type and thus does notrequire a back light. Therefore, a thinner display portion than a liquidcrystal display can be obtained. Note that the light-emitting elementdisplay device includes all display devices for information display suchas personal computer, TV broadcast receiving, and advertisement display.

FIG. 13B is a digital still camera, which is composed of a main body3101, a display portion 3102, an image-receiving portion 3103, operationkeys 3104, external connection ports 3105, a shutter 3106, and the like.The light-emitting device of the present invention can be used in thedisplay portion 3102.

FIG. 13C is a laptop computer, which is composed of a main body 3201, aframe 3202, a display portion 3203, a keyboard 3204, external connectionports 3205, a pointing mouse 3206, and the like. The light-emittingdevice of the present invention can be used in the display portion 3203.

FIG. 13D is a mobile computer, which is composed of a main body 3301, adisplay portion 3302, a switch 3303, operation keys 3304, an infraredport 3305, and the like. The light-emitting device of the presentinvention can be used in the display portion 3302.

FIG. 13E is a portable image reproducing device equipped with arecording medium (specifically, a DVD player), and is composed of a mainbody 3401, a frame 3402, a display portion A 3403, a display portion B3404, a recording medium (such as a DVD) read-in portion 3405, operationkeys 3406, a speaker portion 3407, and the like. The display portion A3403 mainly displays image information, and the display portion B 3404mainly displays character information, and the light-emitting device ofthe present invention can be used in the display portion A 3403 and inthe display portion B 3404. Note that family game machines and the likeare included in the category of image reproducing devices provided witha recording medium.

FIG. 13F is a goggle type display device (head mounted display), whichis composed of a main body 3501, a display portion 3502, and an armportion 3503. The light-emitting device of the present invention can beused in the display portion 3502.

FIG. 13G is a video camera, which is composed of a main body 3601, adisplay portion 3602, a frame 3603, external connection ports 3604, aremote control receiving portion 3605, an image receiving portion 3606,a battery 3607, an audio input portion 3608, operation keys 3609, andthe like. The light-emitting device of the present invention can be usedin the display portion 3602.

FIG. 13H is a mobile telephone, which is composed of a main body 3701, aframe 3702, a display portion 3703, an audio input portion 3704, anaudio output portion 3705, operation keys 3706, external connectionports 3707, an antenna 3708, and the like. The light-emitting device ofthe present invention can be used in the display portion 3703. Note thatwhite characters are displayed on a black background in the displayportion 3703, and thus, the power consumption of the mobile telephonecan be suppressed.

Note that, when a light emitting intensity of an organic light emittingmaterial is increased in future, it can be used for a front type or arear type projector for magnifying and projecting outputted lightincluding image information by a lens or the like. Also, in the aboveelectronic apparatuses, the number of cases where informationdistributed through an electronic communication line such as an Internetor a CATV (cable television) is displayed is increased. In particular, achance in which moving image information is displayed is increased. Aresponse speed of the organic light emitting material is very high.Thus, the light-emitting device is preferable for moving image display.

Also, with respect to the light-emitting device, power is consumed in aportion that emits light. Thus, it is desirable that information isdisplayed so as to minimize an area of a light-emitting portion.Accordingly, when the light-emitting device is used for a displayportion of, a portable information terminal, particularly, a mobiletelephone or a sound reproducing device in which character informationis mainly displayed, it is desirable that the light-emitting device isdriven so as to use a non-light emitting portion as a background andproduce character information in a light emitting portion.

As described above, an application area of the present invention isextremely wide and the light-emitting device can be used for electronicapparatuses in all fields. In addition, the light-emitting device havingany structure described in Embodiments 1 to 7 may be used for theelectronic apparatuses of this embodiment.

Embodiment 7

A phenomenon is used in the present invention as a method of correctingthe threshold value of transistors by making a short circuit between thegate and the drain of a transistor used in correction, and lettingelectric current flow between the source and the drain in this diodestate, thus making the voltage between the source and the drain equal tothe threshold value. It is also possible to apply this phenomenon todriver circuits as well as to pixel portions as introduced by thepresent invention.

An electric current source circuit in a driver circuit for outputtingelectric current to pixels and the like can be given as an example. Theelectric current source circuit is a circuit in which a predeterminedamount of electric current is output in accordance with an input voltagesignal. A voltage signal is input to a gate electrode of an electriccurrent source transistor within the electric current source circuit,and an electric current corresponding to the voltage between the gateand the source is output through the electric current source transistor.That is, the method of the present invention for correcting thethreshold value is utilized in correcting the threshold value of theelectric current source transistor.

An example of utilizing the electric current source circuit is shown inFIG. 23A. Sampling pulses are output in order from a shift register, andthe sampling pulses are each input to electric current source circuits9001. Sampling of an image signal is performed in accordance with thetiming at which the sampling pulses are input to the electric currentsource circuits 9001. Sampling operations are performed in a dotsequential manner in this case.

A simple operation timing is shown in FIG. 23B. A period for selecting anumber i gate signal line is divided into a period for performingsampling of an image signal, in which the sampling pulses are outputfrom the shift register, and a retrace period. The threshold valuecorrection operations of the present invention are performed in theretrace period. That is, operations for initializing the electricpotential of each portion, and operations for obtaining the transistorthreshold voltages are performed sequentially. In other words,operations for obtaining the threshold values can be performed persingle horizontal period.

The structure of a driver circuit for outputting electric current topixels, but which differs from the structure of FIGS. 23A and 23B, isshown in FIG. 24A. Differing from the case of FIGS. 23A and 23B, theelectric current source circuits 9001, which are controlled by one stageof sampling pulses, become two electric current source circuits 9001Aand 9001B, and both operations are selected by an electric currentsource control signal.

As shown in FIG. 24B, the electric current source control signal may bemade to change every single horizontal period, for example. Operation ofthe electric current source circuits 9001A and 9001B is thus performedso that one of the two circuits performs electric current output topixels and the like while the other circuit performs input of the imagesignal. These operations are switched every row. Sampling operations arethus performed in a line sequential manner in this case.

A driver circuit having another different structure is shown in FIG.25A. The image signal type may be either digital or analog in FIGS. 23Aand 23B, and FIGS. 24A and 24B, but a digital image signal is input withthe structure of FIG. 25A. The input digital image signal is taken in bya first latch circuit in accordance with the output of sampling pulses,and is transferred to a second latch circuit after the input of one rowportion of the image signal is complete. This is later input to theelectric current source circuits 9001A and 9001B, and electric currentsource circuits 9001C. The amounts of electric current value output bythe electric current source circuits 9001A to 9001C differ. For example,the ratio of the electric current values becomes 1:2:4. That is, nelectric current source circuits may be disposed in parallel, the ratioof the electric current values of the circuits may be set as 1:2:4: . .. 2^((n-1)), and the amount of electric current values output can bechanged linearly by combining the electric currents output from each ofthe electric current source circuits.

Operation timing is nearly the same as that shown in FIGS. 23A and 23B.Threshold value correction is performed in the electric current sourcecircuits 9001 within the retrace period during which sampling operationsare not performed, data stored in the latch circuits is transferred, andV-I conversion is performed in the electric current source circuits 9001and electric current is output to pixels. The sampling operations areperformed in a line sequential manner, similar to the structure shown inFIGS. 24A and 24B.

The structure of another driver circuit for outputting electric currentto pixels and the like is shown in FIG. 26A. A digital image signaltaken in by a latch circuit is transferred to a D/A converter circuit bythe input of a latching signal with this structure, and the digitalimage signal is converted to an analog image signal. The analog imagesignal is input to each of the electric current source circuits 9001,which output electric current.

Further, other functions may also be given to this type of D/A convertercircuit, such as gamma correction.

Threshold value correction and latch data transfer are performed withinthe retrace period as shown in FIG. 26B. V-I conversion of a certainrow, and output of electric current to pixels and the like, areperformed during a period for performing sampling operations of the nextrow. The sampling operations are performed in a line sequential manner,similar to the structure shown in FIGS. 24A and 24B.

The present invention is not limited to the structures discussed above,and it is possible to apply the threshold value correcting means of thepresent invention to the case of performing V-I correction by using anelectric current source circuit. Further, a structure in which aplurality of electric current source circuits are disposed in parallel,like the structure shown in FIGS. 24A and 24B, and used by switchingbetween the circuits may also be combined with other structures, such asthose of FIGS. 25A and 25B, and those of FIGS. 26A and 26B.

Dispersion in the threshold values of TFTs can be corrected normally bythe present invention, without being influenced by dispersion and thelike in the capacitance values of capacitor means, etc. In addition,although operations are often performed within one horizontal period inthe case of performing threshold value correction in accordance with thestructures shown in FIGS. 10A and 10B, and FIGS. 11A to 11F, the presentinvention is based on a simple operating principle. The operation timingis also simple, and therefore high speed circuit operations becomepossible. In particular, it becomes possible to display a high qualityimage using an image signal having a very large number of bits whenperforming display by a method in which a digital gray scale method anda time gray scale method are combined.

What is claimed is:
 1. A semiconductor device comprising: alight-emitting element; a first transistor; a second transistor; a thirdtransistor; a fourth transistor; a fifth transistor; and a capacitor,wherein one of a source or a drain of the first transistor iselectrically connected to the light-emitting element, wherein a firstelectrode of the capacitor is directly connected to a gate of the firsttransistor, wherein a second electrode of the capacitor is directlyconnected to one of a source or a drain of the second transistor,wherein one of a source or a drain of the third transistor is directlyconnected to the gate of the first transistor, wherein the one of thesource or the drain of the third transistor is directly connected to agate of the third transistor, wherein one of a source or a drain of thefourth transistor is directly connected to the gate of the firsttransistor, and wherein one of a source or a drain of the fifthtransistor is directly connected to the second electrode of thecapacitor.
 2. The semiconductor device according to claim 1, wherein theother of the source or the drain of the first transistor is electricallyconnected to a first line, wherein the other of the source or the drainof the second transistor is electrically connected to a second line, andwherein the other of the source or the drain of the third transistor iselectrically connected to a third line.
 3. The semiconductor deviceaccording to claim 2, wherein the first line is a current supply line,wherein the second line is a source signal line, and wherein the thirdline is a reset electric power source line.
 4. The semiconductor deviceaccording to claim 2, wherein the other of the source or the drain ofthe fourth transistor is electrically connected to the second line. 5.The semiconductor device according to claim 2, wherein the other of thesource or the drain of the fifth transistor is electrically connected tothe first line.
 6. The semiconductor device according to claim 1,wherein the one of the source or the drain of the first transistor isdirectly connected to the light-emitting element.
 7. A light-emittingdevice comprising the semiconductor device according to claim 1 and aflexible printed circuit electrically connected to the semiconductordevice.
 8. An electronic apparatus comprising the light-emitting deviceaccording to claim 7 and at least one selected from the group consistingof a speaker portion, an image receiving portion, an operation key, abattery and an antenna.
 9. A semiconductor device comprising: alight-emitting element; a first transistor; a second transistor; a thirdtransistor; a fourth transistor; and a capacitor, wherein one of asource or a drain of the first transistor is electrically connected tothe light-emitting element, wherein the other of the source or the drainof the first transistor is directly connected to a first line, wherein afirst electrode of the capacitor is directly connected to a gate of thefirst transistor, wherein a second electrode of the capacitor isdirectly connected to one of a source or a drain of the secondtransistor, wherein the one of the source or the drain of the firsttransistor is not directly connected to the second electrode of thecapacitor, wherein the other of the source or the drain of the firsttransistor is not directly connected to the second electrode of thecapacitor, wherein one of a source or a drain of the third transistor isdirectly connected to the gate of the first transistor, and wherein oneof a source or a drain of the fourth transistor is directly connected tothe second electrode of the capacitor.
 10. The semiconductor deviceaccording to claim 9, wherein the other of the source or the drain ofthe second transistor is electrically connected to a second line. 11.The semiconductor device according to claim 10, wherein the first lineis a current supply line, and wherein the second line is a source signalline.
 12. The semiconductor device according to claim 10, wherein theother of the source or the drain of the third transistor is electricallyconnected to the second line.
 13. The semiconductor device according toclaim 10, wherein the other of the source or the drain of the fourthtransistor is electrically connected to the first line.
 14. Thesemiconductor device according to claim 9, wherein the one of the sourceor the drain of the first transistor is directly connected to thelight-emitting element.
 15. A light-emitting device comprising thesemiconductor device according to claim 9 and a flexible printed circuitelectrically connected to the semiconductor device.
 16. An electronicapparatus comprising the light-emitting device according to claim 15 andat least one selected from the group consisting of a speaker portion, animage receiving portion, an operation key, a battery and an antenna.